diff --git a/publication/6-rec/Overview.html b/publication/6-rec/Overview.html
index 665f1f01..55772457 100644
--- a/publication/6-rec/Overview.html
+++ b/publication/6-rec/Overview.html
@@ -159,7 +159,7 @@
   "name": "Web of Things (WoT) Discovery",
   "inLanguage": "en-US",
   "license": "https://www.w3.org/copyright/software-license-2023/",
-  "datePublished": "2023-11-30",
+  "datePublished": "2023-12-05",
   "copyrightHolder": {
     "name": "World Wide Web Consortium",
     "url": "https://www.w3.org/"
@@ -986,7 +986,7 @@
   "inlineCSS": true,
   "noIDLIn": true,
   "specStatus": "REC",
-  "publishDate": "2023-11-30",
+  "publishDate": "2023-12-05",
   "implementationReportURI": "https://w3c.github.io/wot-discovery/testing/report.html",
   "errata": "https://w3c.github.io/wot-discovery/errata.html",
   "shortName": "wot-discovery",
@@ -1133,8 +1133,8 @@
       "id": "amplification-attacks"
     }
   },
-  "publishISODate": "2023-11-30T00:00:00.000Z",
-  "generatedSubtitle": "W3C Recommendation 30 November 2023"
+  "publishISODate": "2023-12-05T00:00:00.000Z",
+  "generatedSubtitle": "W3C Recommendation 05 December 2023"
   }
   </script>
   <link rel="stylesheet" href=
@@ -1149,7 +1149,7 @@
     <h1 id="title" class="title">Web of Things (WoT) Discovery</h1>
     <p id="w3c-state"><a href=
     "https://www.w3.org/standards/types#REC">W3C Recommendation</a>
-    <time class="dt-published" datetime="2023-11-30">30 November
+    <time class="dt-published" datetime="2023-12-05">05 December
     2023</time></p>
     <details open="">
       <summary>
@@ -1159,7 +1159,7 @@ <h1 id="title" class="title">Web of Things (WoT) Discovery</h1>
         <dt>This version:</dt>
         <dd>
           <a class="u-url" href=
-          "https://www.w3.org/TR/2023/REC-wot-discovery-20231130/">https://www.w3.org/TR/2023/REC-wot-discovery-20231130/</a>
+          "https://www.w3.org/TR/2023/REC-wot-discovery-20231205/">https://www.w3.org/TR/2023/REC-wot-discovery-20231205/</a>
         </dd>
         <dt>Latest published version:</dt>
         <dd>
@@ -7162,8 +7162,8 @@ <h3 id="d-1-normative-references"><bdi class=
           "https://www.w3.org/TR/wot-architecture11/"><cite>Web of
           Things (WoT) Architecture 1.1</cite></a>. Michael
           Lagally; Ryuichi Matsukura; Kunihiko Toumura; Michael
-          McCool. W3C. 30 November 2023. W3C Proposed
-          Recommendation. URL: <a href=
+          McCool. W3C. 5 December 2023. W3C Proposed Recommendation.
+          URL: <a href=
           "https://www.w3.org/TR/wot-architecture11/">https://www.w3.org/TR/wot-architecture11/</a>
         </dd>
         <dt id="bib-wot-thing-description11">
@@ -7172,8 +7172,8 @@ <h3 id="d-1-normative-references"><bdi class=
           <a href=
           "https://www.w3.org/TR/wot-thing-description11/"><cite>Web
           of Things (WoT) Thing Description 1.1</cite></a>.
-          Sebastian Käbisch; Michael McCool; Ege Korkan. W3C. 30
-          November 2023. W3C Proposed Recommendation. URL: <a href=
+          Sebastian Käbisch; Michael McCool; Ege Korkan. W3C. 5
+          December 2023. W3C Proposed Recommendation. URL: <a href=
           "https://www.w3.org/TR/wot-thing-description11/">https://www.w3.org/TR/wot-thing-description11/</a>
         </dd>
         <dt id="bib-wot-usecases">[wot-usecases]</dt>
@@ -8022,7 +8022,7 @@ <h3 id="d-2-informative-references"><bdi class=
   panel.classList.remove("docked");
   }
   })()
-  </script> 
+  </script>
   <script src=
   "https://www.w3.org/scripts/TR/2021/fixup.js"></script>
 </body>
diff --git a/publication/6-rec/diff.html b/publication/6-rec/diff.html
index ab6e0c50..e003c8cc 100644
--- a/publication/6-rec/diff.html
+++ b/publication/6-rec/diff.html
@@ -175,7 +175,7 @@
   "name": "Web of Things (WoT) Discovery",
   "inLanguage": "en-US",
   "license": "https://www.w3.org/copyright/software-license-2023/",
-  "datePublished": "2023-11-30",
+  "datePublished": "2023-12-05",
   "copyrightHolder": {
     "name": "World Wide Web Consortium",
     "url": "https://www.w3.org/"
@@ -1010,7 +1010,7 @@
   "inlineCSS": true,
   "noIDLIn": true,
   "specStatus": "REC",
-  "publishDate": "2023-11-30",
+  "publishDate": "2023-12-05",
   "implementationReportURI": "https://w3c.github.io/wot-discovery/testing/report.html",
   "errata": "https://w3c.github.io/wot-discovery/errata.html",
   "shortName": "wot-discovery",
@@ -1157,8 +1157,8 @@
       "id": "amplification-attacks"
     }
   },
-  "publishISODate": "2023-11-30T00:00:00.000Z",
-  "generatedSubtitle": "W3C Recommendation 30 November 2023"
+  "publishISODate": "2023-12-05T00:00:00.000Z",
+  "generatedSubtitle": "W3C Recommendation 05 December 2023"
   }
 ]]>
 </script>
@@ -1208,9 +1208,9 @@ <h1 id="title" class="title">
 <del class="diff-old">11
 July
 </del>
-<time class="dt-published" datetime="2023-11-30">
-<ins class="diff-chg">30
-November
+<time class="dt-published" datetime="2023-12-05">
+<ins class="diff-chg">05
+December
 </ins>
 2023
 </time>
@@ -1231,8 +1231,8 @@ <h1 id="title" class="title">
 <dd>
 <del class="diff-old">https://www.w3.org/TR/2023/PR-wot-discovery-20230711/
 </del>
-<a class="u-url" href= "https://www.w3.org/TR/2023/REC-wot-discovery-20231130/">
-<ins class="diff-chg">https://www.w3.org/TR/2023/REC-wot-discovery-20231130/
+<a class="u-url" href= "https://www.w3.org/TR/2023/REC-wot-discovery-20231205/">
+<ins class="diff-chg">https://www.w3.org/TR/2023/REC-wot-discovery-20231205/
 </ins>
 </a>
 </dd>
@@ -23740,8 +23740,8 @@ <h3 id="d-1-normative-references">
 <del class="diff-old">19
 January
 </del>
-<ins class="diff-chg">30
-November
+<ins class="diff-chg">11
+July
 </ins>
 2023.
 W3C
@@ -23780,8 +23780,8 @@ <h3 id="d-1-normative-references">
 <del class="diff-old">19
 January
 </del>
-<ins class="diff-chg">30
-November
+<ins class="diff-chg">11
+July
 </ins>
 2023.
 W3C
diff --git a/publication/6-rec/diff2.html b/publication/6-rec/diff2.html
new file mode 100644
index 00000000..38d2e175
--- /dev/null
+++ b/publication/6-rec/diff2.html
@@ -0,0 +1,25607 @@
+<!DOCTYPE html>
+<html lang="en-US" xmlns="http://www.w3.org/1999/xhtml" xml:lang=
+"en-US">
+<head>
+<meta name="generator" content=
+"HTML Tidy for HTML5 for Linux version 5.7.27" />
+<meta charset="utf-8" />
+<meta name="generator" content="ReSpec 34.2.2" />
+<meta name="viewport" content=
+"width=device-width, initial-scale=1, shrink-to-fit=no" />
+<style>
+<![CDATA[
+  span.example-title{text-transform:none}
+  :is(aside,div).example,div.illegal-example{padding:.5em;margin:1em 0;position:relative;clear:both}
+  div.illegal-example{color:red}
+  div.illegal-example p{color:#000}
+  :is(aside,div).example{border-left-width:.5em;border-left-style:solid;border-color:#e0cb52;background:#fcfaee}
+  aside.example div.example{border-left-width:.1em;border-color:#999;background:#fff}
+  .example pre{background-color:rgba(0,0,0,.03)}
+]]>
+</style>
+
+<style>
+<![CDATA[
+  .issue-label{text-transform:initial}
+  .warning>p:first-child{margin-top:0}
+  .warning{padding:.5em;border-left-width:.5em;border-left-style:solid}
+  span.warning{padding:.1em .5em .15em}
+  .issue.closed span.issue-number{text-decoration:line-through}
+  .issue.closed span.issue-number::after{content:" (Closed)";font-size:smaller}
+  .warning{border-color:#f11;border-width:.2em;border-style:solid;background:#fbe9e9}
+  .warning-title:before{content:"⚠";font-size:1.3em;float:left;padding-right:.3em;margin-top:-.3em}
+  li.task-list-item{list-style:none}
+  input.task-list-item-checkbox{margin:0 .35em .25em -1.6em;vertical-align:middle}
+  .issue a.respec-gh-label{padding:5px;margin:0 2px 0 2px;font-size:10px;text-transform:none;text-decoration:none;font-weight:700;border-radius:4px;position:relative;bottom:2px;border:none;display:inline-block}
+]]>
+</style>
+
+<style>
+<![CDATA[
+  dfn{cursor:pointer}
+  .dfn-panel{position:absolute;z-index:35;min-width:300px;max-width:500px;padding:.5em .75em;margin-top:.6em;font-family:"Helvetica Neue",sans-serif;font-size:small;background:#fff;color:#000;box-shadow:0 1em 3em -.4em rgba(0,0,0,.3),0 0 1px 1px rgba(0,0,0,.05);border-radius:2px}
+  .dfn-panel:not(.docked)>.caret{position:absolute;top:-9px}
+  .dfn-panel:not(.docked)>.caret::after,.dfn-panel:not(.docked)>.caret::before{content:"";position:absolute;border:10px solid transparent;border-top:0;border-bottom:10px solid #fff;top:0}
+  .dfn-panel:not(.docked)>.caret::before{border-bottom:9px solid #a2a9b1}
+  .dfn-panel *{margin:0}
+  .dfn-panel b{display:block;color:#000;margin-top:.25em}
+  .dfn-panel ul a[href]{color:#333}
+  .dfn-panel>div{display:flex}
+  .dfn-panel a.self-link{font-weight:700;margin-right:auto}
+  .dfn-panel .marker{padding:.1em;margin-left:.5em;border-radius:.2em;text-align:center;white-space:nowrap;font-size:90%;color:#040b1c}
+  .dfn-panel .marker.dfn-exported{background:#d1edfd;box-shadow:0 0 0 .125em #1ca5f940}
+  .dfn-panel .marker.idl-block{background:#8ccbf2;box-shadow:0 0 0 .125em #0670b161}
+  .dfn-panel a:not(:hover){text-decoration:none!important;border-bottom:none!important}
+  .dfn-panel a[href]:hover{border-bottom-width:1px}
+  .dfn-panel ul{padding:0}
+  .dfn-panel li{margin-left:1em}
+  .dfn-panel.docked{position:fixed;left:.5em;top:unset;bottom:2em;margin:0 auto;max-width:calc(100vw - .75em * 2 - .5em - .2em * 2);max-height:30vh;overflow:auto}
+]]>
+</style>
+<title>Web of Things (WoT) Discovery</title>
+
+<style>
+<![CDATA[
+
+  a[href].internalDFN {
+        color: inherit;
+        border-bottom: 1px solid #99c;
+        text-decoration: none;
+  }
+  img.wot-diagram {
+    max-width: 90%;
+    height: auto;
+  }
+  .rfc2119-assertion {
+  background-color: rgb(230,230,230)
+  }
+
+]]>
+</style>
+
+<style id="respec-mainstyle">
+<![CDATA[
+  @keyframes pop{
+  0%{transform:scale(1,1)}
+  25%{transform:scale(1.25,1.25);opacity:.75}
+  100%{transform:scale(1,1)}
+  }
+  :is(h1,h2,h3,h4,h5,h6,a) abbr{border:none}
+  dfn{font-weight:700}
+  a.internalDFN{color:inherit;border-bottom:1px solid #99c;text-decoration:none}
+  a.externalDFN{color:inherit;border-bottom:1px dotted #ccc;text-decoration:none}
+  a.bibref{text-decoration:none}
+  .respec-offending-element:target{animation:pop .25s ease-in-out 0s 1}
+  .respec-offending-element,a[href].respec-offending-element{text-decoration:red wavy underline}
+  @supports not (text-decoration:red wavy underline){
+  .respec-offending-element:not(pre){display:inline-block}
+  .respec-offending-element{background:url(data:image/gif;base64,R0lGODdhBAADAPEAANv///8AAP///wAAACwAAAAABAADAEACBZQjmIAFADs=) bottom repeat-x}
+  }
+  #references :target{background:#eaf3ff;animation:pop .4s ease-in-out 0s 1}
+  cite .bibref{font-style:normal}
+  a[href].orcid{padding-left:4px;padding-right:4px}
+  a[href].orcid>svg{margin-bottom:-2px}
+  .toc a,.tof a{text-decoration:none}
+  a .figno,a .secno{color:#000}
+  ol.tof,ul.tof{list-style:none outside none}
+  .caption{margin-top:.5em;font-style:italic}
+  table.simple{border-spacing:0;border-collapse:collapse;border-bottom:3px solid #005a9c}
+  .simple th{background:#005a9c;color:#fff;padding:3px 5px;text-align:left}
+  .simple th a{color:#fff;padding:3px 5px;text-align:left}
+  .simple th[scope=row]{background:inherit;color:inherit;border-top:1px solid #ddd}
+  .simple td{padding:3px 10px;border-top:1px solid #ddd}
+  .simple tr:nth-child(even){background:#f0f6ff}
+  .section dd>p:first-child{margin-top:0}
+  .section dd>p:last-child{margin-bottom:0}
+  .section dd{margin-bottom:1em}
+  .section dl.attrs dd,.section dl.eldef dd{margin-bottom:0}
+  #issue-summary>ul{column-count:2}
+  #issue-summary li{list-style:none;display:inline-block}
+  details.respec-tests-details{margin-left:1em;display:inline-block;vertical-align:top}
+  details.respec-tests-details>*{padding-right:2em}
+  details.respec-tests-details[open]{z-index:999999;position:absolute;border:thin solid #cad3e2;border-radius:.3em;background-color:#fff;padding-bottom:.5em}
+  details.respec-tests-details[open]>summary{border-bottom:thin solid #cad3e2;padding-left:1em;margin-bottom:1em;line-height:2em}
+  details.respec-tests-details>ul{width:100%;margin-top:-.3em}
+  details.respec-tests-details>li{padding-left:1em}
+  .self-link:hover{opacity:1;text-decoration:none;background-color:transparent}
+  aside.example .marker>a.self-link{color:inherit}
+  .header-wrapper{display:flex;align-items:baseline}
+  :is(h2,h3,h4,h5,h6):not(#toc>h2,#abstract>h2,#sotd>h2,.head>h2){position:relative;left:-.5em}
+  :is(h2,h3,h4,h5,h6):not(#toch2)+a.self-link{color:inherit;order:-1;position:relative;left:-1.1em;font-size:1rem;opacity:.5}
+  :is(h2,h3,h4,h5,h6)+a.self-link::before{content:"§";text-decoration:none;color:var(--heading-text)}
+  :is(h2,h3)+a.self-link{top:-.2em}
+  :is(h4,h5,h6)+a.self-link::before{color:#000}
+  @media (max-width:767px){
+  dd{margin-left:0}
+  }
+  @media print{
+  .removeOnSave{display:none}
+  }
+]]>
+</style>
+<meta name="description" content=
+"The W3C Web of Things (WoT) is intended to enable interoperability across IoT platforms and application domains. One key mechanism for accomplishing this goal is the definition and use of metadata describing the interactions an IoT device or service makes available over the network at a suitable level of abstraction. The WoT Thing Description specification satisfies this objective." />
+<link rel="canonical" href=
+"https://www.w3.org/TR/wot-discovery/" />
+<script type="application/ld+json">
+<![CDATA[
+  {
+  "@context": [
+    "http://schema.org",
+    {
+      "@vocab": "http://schema.org/",
+      "@language": "en-US",
+      "w3p": "http://www.w3.org/2001/02pd/rec54#",
+      "foaf": "http://xmlns.com/foaf/0.1/",
+      "datePublished": {
+        "@type": "http://www.w3.org/2001/XMLSchema#date"
+      },
+      "inLanguage": {
+        "@language": null
+      },
+      "isBasedOn": {
+        "@type": "@id"
+      },
+      "license": {
+        "@type": "@id"
+      }
+    }
+  ],
+  "id": "https://www.w3.org/TR/wot-discovery/",
+  "type": [
+    "TechArticle",
+    "w3p:REC"
+  ],
+  "name": "Web of Things (WoT) Discovery",
+  "inLanguage": "en-US",
+  "license": "https://www.w3.org/copyright/software-license-2023/",
+  "datePublished": "2023-12-05",
+  "copyrightHolder": {
+    "name": "World Wide Web Consortium",
+    "url": "https://www.w3.org/"
+  },
+  "discussionUrl": "https://github.com/w3c/wot-discovery/issues/",
+  "alternativeHeadline": "",
+  "isBasedOn": "https://www.w3.org/TR/2023/PR-wot-discovery-20230711/",
+  "description": "The W3C Web of Things (WoT) is intended to enable\n           interoperability across IoT platforms and application\n           domains.  One key mechanism for accomplishing this goal\n           is the definition and use of metadata describing the\n           interactions an IoT device or service makes available\n           over the network at a suitable level of abstraction.  \n           The WoT Thing Description specification satisfies this objective.",
+  "editor": [
+    {
+      "type": "Person",
+      "name": "Andrea Cimmino",
+      "worksFor": {
+        "name": "Universidad Politécnica de Madrid",
+        "url": "https://www.upm.es/"
+      }
+    },
+    {
+      "type": "Person",
+      "name": "Michael McCool",
+      "worksFor": {
+        "name": "Intel Corp.",
+        "url": "https://www.intel.com/"
+      }
+    },
+    {
+      "type": "Person",
+      "name": "Farshid Tavakolizadeh",
+      "worksFor": {
+        "name": "Invited Expert"
+      }
+    },
+    {
+      "type": "Person",
+      "name": "Kunihiko Toumura",
+      "worksFor": {
+        "name": "Hitachi, Ltd.",
+        "url": "https://www.hitachi.com/"
+      }
+    }
+  ],
+  "contributor": [],
+  "citation": [
+    {
+      "id": "https://www.w3.org/TR/wot-architecture11/",
+      "type": "TechArticle",
+      "name": "Web of Things (WoT) Architecture 1.1",
+      "url": "https://www.w3.org/TR/wot-architecture11/",
+      "creator": [
+        {
+          "name": "Michael Lagally"
+        },
+        {
+          "name": "Ryuichi Matsukura"
+        },
+        {
+          "name": "Kunihiko Toumura"
+        },
+        {
+          "name": "Michael McCool"
+        }
+      ],
+      "publisher": {
+        "name": "W3C"
+      }
+    },
+    {
+      "id": "https://www.w3.org/TR/wot-thing-description11/",
+      "type": "TechArticle",
+      "name": "Web of Things (WoT) Thing Description 1.1",
+      "url": "https://www.w3.org/TR/wot-thing-description11/",
+      "creator": [
+        {
+          "name": "Sebastian Käbisch"
+        },
+        {
+          "name": "Michael McCool"
+        },
+        {
+          "name": "Ege Korkan"
+        }
+      ],
+      "publisher": {
+        "name": "W3C"
+      }
+    },
+    {
+      "id": "https://dl.acm.org/doi/10.1145/2991561.2991570",
+      "type": "TechArticle",
+      "name": "A Categorization of Discovery Technologies for the Internet of Things",
+      "url": "https://dl.acm.org/doi/10.1145/2991561.2991570",
+      "creator": [
+        {
+          "name": "Arne Broering"
+        },
+        {
+          "name": "Soumya Kanti Datta"
+        },
+        {
+          "name": "Christian Bonnet"
+        }
+      ],
+      "publisher": {
+        "name": "Association of Computing Machinery (ACM): IoT'16 Proceedings"
+      }
+    },
+    {
+      "id": "https://www.w3.org/TR/sparql11-overview/",
+      "type": "TechArticle",
+      "name": "SPARQL 1.1 Overview",
+      "url": "https://www.w3.org/TR/sparql11-overview/",
+      "creator": [
+        {
+          "name": "The W3C SPARQL Working Group"
+        }
+      ],
+      "publisher": {
+        "name": "W3C"
+      }
+    },
+    {
+      "id": "https://w3c.github.io/wot-usecases/",
+      "type": "TechArticle",
+      "name": "Web of Things (WoT): Use Cases",
+      "url": "https://w3c.github.io/wot-usecases/",
+      "creator": [
+        {
+          "name": "Michael Lagally"
+        },
+        {
+          "name": "Michael McCool"
+        },
+        {
+          "name": "Ryuichi Matsukura"
+        },
+        {
+          "name": "Tomoaki Mizushima"
+        }
+      ],
+      "publisher": {
+        "name": "W3C"
+      }
+    },
+    {
+      "id": "https://www.rfc-editor.org/rfc/rfc8615",
+      "type": "TechArticle",
+      "name": "Well-Known Uniform Resource Identifiers (URIs)",
+      "url": "https://www.rfc-editor.org/rfc/rfc8615",
+      "creator": [
+        {
+          "name": "M. Nottingham"
+        }
+      ],
+      "publisher": {
+        "name": "IETF"
+      }
+    },
+    {
+      "id": "https://www.rfc-editor.org/rfc/rfc6763",
+      "type": "TechArticle",
+      "name": "DNS-Based Service Discovery",
+      "url": "https://www.rfc-editor.org/rfc/rfc6763",
+      "creator": [
+        {
+          "name": "S. Cheshire"
+        },
+        {
+          "name": "M. Krochmal"
+        }
+      ],
+      "publisher": {
+        "name": "IETF"
+      }
+    },
+    {
+      "id": "https://www.rfc-editor.org/rfc/rfc6762",
+      "type": "TechArticle",
+      "name": "Multicast DNS",
+      "url": "https://www.rfc-editor.org/rfc/rfc6762",
+      "creator": [
+        {
+          "name": "S. Cheshire"
+        },
+        {
+          "name": "M. Krochmal"
+        }
+      ],
+      "publisher": {
+        "name": "IETF"
+      }
+    },
+    {
+      "id": "https://www.rfc-editor.org/rfc/rfc7595",
+      "type": "TechArticle",
+      "name": "Guidelines and Registration Procedures for URI Schemes",
+      "url": "https://www.rfc-editor.org/rfc/rfc7595",
+      "creator": [
+        {
+          "name": "D. Thaler, Ed."
+        },
+        {
+          "name": "T. Hansen"
+        },
+        {
+          "name": "T. Hardie"
+        }
+      ],
+      "publisher": {
+        "name": "IETF"
+      }
+    },
+    {
+      "id": "https://www.rfc-editor.org/rfc/rfc6690",
+      "type": "TechArticle",
+      "name": "Constrained RESTful Environments (CoRE) Link Format",
+      "url": "https://www.rfc-editor.org/rfc/rfc6690",
+      "creator": [
+        {
+          "name": "Z. Shelby"
+        }
+      ],
+      "publisher": {
+        "name": "IETF"
+      }
+    },
+    {
+      "id": "https://www.rfc-editor.org/rfc/rfc9176",
+      "type": "TechArticle",
+      "name": "Constrained RESTful Environments (CoRE) Resource Directory",
+      "url": "https://www.rfc-editor.org/rfc/rfc9176",
+      "creator": [
+        {
+          "name": "C. Amsüss, Ed."
+        },
+        {
+          "name": "Z. Shelby"
+        },
+        {
+          "name": "M. Koster"
+        },
+        {
+          "name": "C. Bormann"
+        },
+        {
+          "name": "P. van der Stok"
+        }
+      ],
+      "publisher": {
+        "name": "IETF"
+      }
+    },
+    {
+      "id": "https://www.w3.org/TR/did-core/",
+      "type": "TechArticle",
+      "name": "Decentralized Identifiers (DIDs) v1.0",
+      "url": "https://www.w3.org/TR/did-core/",
+      "creator": [
+        {
+          "name": "Manu Sporny"
+        },
+        {
+          "name": "Amy Guy"
+        },
+        {
+          "name": "Markus Sabadello"
+        },
+        {
+          "name": "Drummond Reed"
+        }
+      ],
+      "publisher": {
+        "name": "W3C"
+      }
+    },
+    {
+      "id": "https://www.w3.org/TR/did-spec-registries/",
+      "type": "TechArticle",
+      "name": "DID Specification Registries",
+      "url": "https://www.w3.org/TR/did-spec-registries/",
+      "creator": [
+        {
+          "name": "Orie Steele"
+        },
+        {
+          "name": "Manu Sporny"
+        }
+      ],
+      "publisher": {
+        "name": "W3C"
+      }
+    },
+    {
+      "id": "https://www.w3.org/TR/json-ld11/",
+      "type": "TechArticle",
+      "name": "JSON-LD 1.1",
+      "url": "https://www.w3.org/TR/json-ld11/",
+      "creator": [
+        {
+          "name": "Gregg Kellogg"
+        },
+        {
+          "name": "Pierre-Antoine Champin"
+        },
+        {
+          "name": "Dave Longley"
+        }
+      ],
+      "publisher": {
+        "name": "W3C"
+      }
+    },
+    {
+      "id": "https://www.rfc-editor.org/rfc/rfc7959",
+      "type": "TechArticle",
+      "name": "Block-Wise Transfers in the Constrained Application Protocol (CoAP)",
+      "url": "https://www.rfc-editor.org/rfc/rfc7959",
+      "creator": [
+        {
+          "name": "C. Bormann"
+        },
+        {
+          "name": "Z. Shelby, Ed."
+        }
+      ],
+      "publisher": {
+        "name": "IETF"
+      }
+    },
+    {
+      "id": "https://www.rfc-editor.org/rfc/rfc3339",
+      "type": "TechArticle",
+      "name": "Date and Time on the Internet: Timestamps",
+      "url": "https://www.rfc-editor.org/rfc/rfc3339",
+      "creator": [
+        {
+          "name": "G. Klyne"
+        },
+        {
+          "name": "C. Newman"
+        }
+      ],
+      "publisher": {
+        "name": "IETF"
+      }
+    },
+    {
+      "id": "https://www.rfc-editor.org/rfc/rfc4122",
+      "type": "TechArticle",
+      "name": "A Universally Unique IDentifier (UUID) URN Namespace",
+      "url": "https://www.rfc-editor.org/rfc/rfc4122",
+      "creator": [
+        {
+          "name": "P. Leach"
+        },
+        {
+          "name": "M. Mealling"
+        },
+        {
+          "name": "R. Salz"
+        }
+      ],
+      "publisher": {
+        "name": "IETF"
+      }
+    },
+    {
+      "id": "https://www.rfc-editor.org/rfc/rfc7807",
+      "type": "TechArticle",
+      "name": "Problem Details for HTTP APIs",
+      "url": "https://www.rfc-editor.org/rfc/rfc7807",
+      "creator": [
+        {
+          "name": "M. Nottingham"
+        },
+        {
+          "name": "E. Wilde"
+        }
+      ],
+      "publisher": {
+        "name": "IETF"
+      }
+    },
+    {
+      "id": "https://httpwg.org/specs/rfc7231.html",
+      "type": "TechArticle",
+      "name": "Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content",
+      "url": "https://httpwg.org/specs/rfc7231.html",
+      "creator": [
+        {
+          "name": "R. Fielding, Ed."
+        },
+        {
+          "name": "J. Reschke, Ed."
+        }
+      ],
+      "publisher": {
+        "name": "IETF"
+      }
+    },
+    {
+      "id": "https://www.rfc-editor.org/rfc/rfc1738",
+      "type": "TechArticle",
+      "name": "Uniform Resource Locators (URL)",
+      "url": "https://www.rfc-editor.org/rfc/rfc1738",
+      "creator": [
+        {
+          "name": "T. Berners-Lee"
+        },
+        {
+          "name": "L. Masinter"
+        },
+        {
+          "name": "M. McCahill"
+        }
+      ],
+      "publisher": {
+        "name": "IETF"
+      }
+    },
+    {
+      "id": "https://www.rfc-editor.org/rfc/rfc7396",
+      "type": "TechArticle",
+      "name": "JSON Merge Patch",
+      "url": "https://www.rfc-editor.org/rfc/rfc7396",
+      "creator": [
+        {
+          "name": "P. Hoffman"
+        },
+        {
+          "name": "J. Snell"
+        }
+      ],
+      "publisher": {
+        "name": "IETF"
+      }
+    },
+    {
+      "id": "https://httpwg.org/specs/rfc8288.html",
+      "type": "TechArticle",
+      "name": "Web Linking",
+      "url": "https://httpwg.org/specs/rfc8288.html",
+      "creator": [
+        {
+          "name": "M. Nottingham"
+        }
+      ],
+      "publisher": {
+        "name": "IETF"
+      }
+    },
+    {
+      "id": "https://html.spec.whatwg.org/multipage/",
+      "type": "TechArticle",
+      "name": "HTML Standard",
+      "url": "https://html.spec.whatwg.org/multipage/",
+      "creator": [
+        {
+          "name": "Anne van Kesteren"
+        },
+        {
+          "name": "Domenic Denicola"
+        },
+        {
+          "name": "Ian Hickson"
+        },
+        {
+          "name": "Philip Jägenstedt"
+        },
+        {
+          "name": "Simon Pieters"
+        }
+      ],
+      "publisher": {
+        "name": "WHATWG"
+      }
+    },
+    {
+      "id": "https://www.w3.org/TR/xpath-31/",
+      "type": "TechArticle",
+      "name": "XML Path Language (XPath) 3.1",
+      "url": "https://www.w3.org/TR/xpath-31/",
+      "creator": [
+        {
+          "name": "Jonathan Robie"
+        },
+        {
+          "name": "Michael Dyck"
+        },
+        {
+          "name": "Josh Spiegel"
+        }
+      ],
+      "publisher": {
+        "name": "W3C"
+      }
+    },
+    {
+      "id": "https://owasp.org/www-project-top-ten/",
+      "type": "TechArticle",
+      "name": "OWASP Top Ten",
+      "url": "https://owasp.org/www-project-top-ten/",
+      "publisher": {
+        "name": "OWASP"
+      }
+    },
+    {
+      "id": "https://datatracker.ietf.org/doc/html/draft-irtf-t2trg-amplification-attacks",
+      "type": "TechArticle",
+      "name": "Amplification Attacks Using the Constrained Application Protocol (CoAP)",
+      "url": "https://datatracker.ietf.org/doc/html/draft-irtf-t2trg-amplification-attacks",
+      "creator": [
+        {
+          "name": "John Preuß Mattsson"
+        },
+        {
+          "name": "Göran Selander"
+        },
+        {
+          "name": "Christian Amsüss"
+        }
+      ],
+      "publisher": {
+        "name": "IETF"
+      }
+    },
+    {
+      "id": "https://www.rfc-editor.org/rfc/rfc9000",
+      "type": "TechArticle",
+      "name": "QUIC: A UDP-Based Multiplexed and Secure Transport",
+      "url": "https://www.rfc-editor.org/rfc/rfc9000",
+      "creator": [
+        {
+          "name": "J. Iyengar, Ed."
+        },
+        {
+          "name": "M. Thomson, Ed."
+        }
+      ],
+      "publisher": {
+        "name": "IETF"
+      }
+    },
+    {
+      "id": "https://www.rfc-editor.org/rfc/rfc4279",
+      "type": "TechArticle",
+      "name": "Pre-Shared Key Ciphersuites for Transport Layer Security (TLS)",
+      "url": "https://www.rfc-editor.org/rfc/rfc4279",
+      "creator": [
+        {
+          "name": "P. Eronen, Ed."
+        },
+        {
+          "name": "H. Tschofenig, Ed."
+        }
+      ],
+      "publisher": {
+        "name": "IETF"
+      }
+    },
+    {
+      "id": "https://gdpr-info.eu/art-4-gdpr/",
+      "type": "TechArticle",
+      "name": "General Data Protection Regulation (GDPR) Article 4 - Definitions",
+      "url": "https://gdpr-info.eu/art-4-gdpr/",
+      "publisher": {
+        "name": "European Union (EU) and the European Economic Area (EEA)"
+      }
+    },
+    {
+      "id": "https://www.rfc-editor.org/rfc/rfc8981",
+      "type": "TechArticle",
+      "name": "Temporary Address Extensions for Stateless Address Autoconfiguration in IPv6",
+      "url": "https://www.rfc-editor.org/rfc/rfc8981",
+      "creator": [
+        {
+          "name": "F. Gont"
+        },
+        {
+          "name": "S. Krishnan"
+        },
+        {
+          "name": "T. Narten"
+        },
+        {
+          "name": "R. Draves"
+        }
+      ],
+      "publisher": {
+        "name": "IETF"
+      }
+    },
+    {
+      "id": "https://www.rfc-editor.org/rfc/rfc6335",
+      "type": "TechArticle",
+      "name": "Internet Assigned Numbers Authority (IANA) Procedures for the Management of the Service Name and Transport Protocol Port Number Registry",
+      "url": "https://www.rfc-editor.org/rfc/rfc6335",
+      "creator": [
+        {
+          "name": "M. Cotton"
+        },
+        {
+          "name": "L. Eggert"
+        },
+        {
+          "name": "J. Touch"
+        },
+        {
+          "name": "M. Westerlund"
+        },
+        {
+          "name": "S. Cheshire"
+        }
+      ],
+      "publisher": {
+        "name": "IETF"
+      }
+    },
+    {
+      "id": "https://www.rfc-editor.org/rfc/rfc2119",
+      "type": "TechArticle",
+      "name": "Key words for use in RFCs to Indicate Requirement Levels",
+      "url": "https://www.rfc-editor.org/rfc/rfc2119",
+      "creator": [
+        {
+          "name": "S. Bradner"
+        }
+      ],
+      "publisher": {
+        "name": "IETF"
+      }
+    },
+    {
+      "id": "https://www.rfc-editor.org/rfc/rfc8174",
+      "type": "TechArticle",
+      "name": "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words",
+      "url": "https://www.rfc-editor.org/rfc/rfc8174",
+      "creator": [
+        {
+          "name": "B. Leiba"
+        }
+      ],
+      "publisher": {
+        "name": "IETF"
+      }
+    },
+    {
+      "id": "https://datatracker.ietf.org/doc/html/draft-irtf-t2trg-rest-iot-06",
+      "type": "TechArticle",
+      "name": "RESTful Design for Internet of Things Systems",
+      "url": "https://datatracker.ietf.org/doc/html/draft-irtf-t2trg-rest-iot-06",
+      "creator": [
+        {
+          "name": "Ari Keranen"
+        },
+        {
+          "name": "Matthias Kovatsch"
+        },
+        {
+          "name": "Klaus Hartke"
+        }
+      ],
+      "publisher": {
+        "name": "IETF"
+      }
+    },
+    {
+      "id": "https://www.w3.org/TR/ldp-paging/",
+      "type": "TechArticle",
+      "name": "Linked Data Platform Paging 1.0",
+      "url": "https://www.w3.org/TR/ldp-paging/",
+      "creator": [
+        {
+          "name": "Steve Speicher"
+        },
+        {
+          "name": "John Arwe"
+        },
+        {
+          "name": "Ashok Malhotra"
+        }
+      ],
+      "publisher": {
+        "name": "W3C"
+      }
+    },
+    {
+      "id": "https://datatracker.ietf.org/doc/html/draft-ietf-jsonpath-base",
+      "type": "TechArticle",
+      "name": "JSONPath: Query expressions for JSON",
+      "url": "https://datatracker.ietf.org/doc/html/draft-ietf-jsonpath-base",
+      "creator": [
+        {
+          "name": "Stefan Gössner"
+        },
+        {
+          "name": "Glyn Normington"
+        },
+        {
+          "name": "Carsten Bormann"
+        }
+      ],
+      "publisher": {
+        "name": "IETF"
+      }
+    },
+    {
+      "id": "https://www.w3.org/TR/wot-security/",
+      "type": "TechArticle",
+      "name": "Web of Things (WoT) Security and Privacy Guidelines",
+      "url": "https://www.w3.org/TR/wot-security/",
+      "creator": [
+        {
+          "name": "Elena Reshetova"
+        },
+        {
+          "name": "Michael McCool"
+        }
+      ],
+      "publisher": {
+        "name": "W3C"
+      }
+    },
+    {
+      "id": "https://httpwg.org/specs/rfc7230.html",
+      "type": "TechArticle",
+      "name": "Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing",
+      "url": "https://httpwg.org/specs/rfc7230.html",
+      "creator": [
+        {
+          "name": "R. Fielding, Ed."
+        },
+        {
+          "name": "J. Reschke, Ed."
+        }
+      ],
+      "publisher": {
+        "name": "IETF"
+      }
+    },
+    {
+      "id": "https://httpwg.org/specs/rfc7540.html",
+      "type": "TechArticle",
+      "name": "Hypertext Transfer Protocol Version 2 (HTTP/2)",
+      "url": "https://httpwg.org/specs/rfc7540.html",
+      "creator": [
+        {
+          "name": "M. Belshe"
+        },
+        {
+          "name": "R. Peon"
+        },
+        {
+          "name": "M. Thomson, Ed."
+        }
+      ],
+      "publisher": {
+        "name": "IETF"
+      }
+    },
+    {
+      "id": "https://www.rfc-editor.org/rfc/rfc8323",
+      "type": "TechArticle",
+      "name": "CoAP (Constrained Application Protocol) over TCP, TLS, and WebSockets",
+      "url": "https://www.rfc-editor.org/rfc/rfc8323",
+      "creator": [
+        {
+          "name": "C. Bormann"
+        },
+        {
+          "name": "S. Lemay"
+        },
+        {
+          "name": "H. Tschofenig"
+        },
+        {
+          "name": "K. Hartke"
+        },
+        {
+          "name": "B. Silverajan"
+        },
+        {
+          "name": "B. Raymor, Ed."
+        }
+      ],
+      "publisher": {
+        "name": "IETF"
+      }
+    }
+  ]
+  }
+]]>
+</script>
+<style>
+<![CDATA[
+  .hljs{display:block;overflow-x:auto;padding:.5em;color:#383a42;background:#fafafa}
+  .hljs-comment,.hljs-quote{color:#717277;font-style:italic}
+  .hljs-doctag,.hljs-formula,.hljs-keyword{color:#a626a4}
+  .hljs-deletion,.hljs-name,.hljs-section,.hljs-selector-tag,.hljs-subst{color:#ca4706;font-weight:700}
+  .hljs-literal{color:#0b76c5}
+  .hljs-addition,.hljs-attribute,.hljs-meta-string,.hljs-regexp,.hljs-string{color:#42803c}
+  .hljs-built_in,.hljs-class .hljs-title{color:#9a6a01}
+  .hljs-attr,.hljs-number,.hljs-selector-attr,.hljs-selector-class,.hljs-selector-pseudo,.hljs-template-variable,.hljs-type,.hljs-variable{color:#986801}
+  .hljs-bullet,.hljs-link,.hljs-meta,.hljs-selector-id,.hljs-symbol,.hljs-title{color:#336ae3}
+  .hljs-emphasis{font-style:italic}
+  .hljs-strong{font-weight:700}
+  .hljs-link{text-decoration:underline}
+]]>
+</style>
+
+<style>
+<![CDATA[
+  var{position:relative;cursor:pointer}
+  var[data-type]::after,var[data-type]::before{position:absolute;left:50%;top:-6px;opacity:0;transition:opacity .4s;pointer-events:none}
+  var[data-type]::before{content:"";transform:translateX(-50%);border-width:4px 6px 0 6px;border-style:solid;border-color:transparent;border-top-color:#000}
+  var[data-type]::after{content:attr(data-type);transform:translateX(-50%) translateY(-100%);background:#000;text-align:center;font-family:"Dank Mono","Fira Code",monospace;font-style:normal;padding:6px;border-radius:3px;color:#daca88;text-indent:0;font-weight:400}
+  var[data-type]:hover::after,var[data-type]:hover::before{opacity:1}
+]]>
+</style>
+
+<script id="initialUserConfig" type="application/json">
+<![CDATA[
+  {
+  "lint": {
+    "check-punctuation": true,
+    "local-refs-exist": true,
+    "no-http-props": true,
+    "no-headingless-sections": true,
+    "no-unused-dfns": false
+  },
+  "doJsonLd": true,
+  "noLegacyStyle": true,
+  "inlineCSS": true,
+  "noIDLIn": true,
+  "specStatus": "REC",
+  "publishDate": "2023-12-05",
+  "implementationReportURI": "https://w3c.github.io/wot-discovery/testing/report.html",
+  "errata": "https://w3c.github.io/wot-discovery/errata.html",
+  "shortName": "wot-discovery",
+  "copyrightStart": 2017,
+  "group": "wg/wot",
+  "wgPublicList": "public-wot-wg",
+  "github": {
+    "repoURL": "https://github.com/w3c/wot-discovery",
+    "branch": "main"
+  },
+  "previousPublishDate": "2023-07-11",
+  "previousMaturity": "PR",
+  "editors": [
+    {
+      "name": "Andrea Cimmino",
+      "w3cid": "115672",
+      "company": "Universidad Politécnica de Madrid",
+      "companyURL": "https://www.upm.es/"
+    },
+    {
+      "name": "Michael McCool",
+      "w3cid": "93137",
+      "company": "Intel Corp.",
+      "companyURL": "https://www.intel.com/"
+    },
+    {
+      "name": "Farshid Tavakolizadeh",
+      "w3cid": "122520",
+      "company": "Invited Expert"
+    },
+    {
+      "name": "Kunihiko Toumura",
+      "w3cid": "83488",
+      "company": "Hitachi, Ltd.",
+      "companyURL": "https://www.hitachi.com/"
+    }
+  ],
+  "formerEditors": [
+    {
+      "name": "Farshid Tavakolizadeh",
+      "w3cid": "122520",
+      "company": "Fraunhofer-Gesellschaft",
+      "companyURL": "https://www.fraunhofer.de/",
+      "retiredDate": "2021-09-30"
+    }
+  ],
+  "otherLinks": [
+    {
+      "key": "Contributors",
+      "data": [
+        {
+          "value": "In the GitHub repository",
+          "href": "https://github.com/w3c/wot-discovery/graphs/contributors"
+        }
+      ]
+    },
+    {
+      "key": "Repository",
+      "data": [
+        {
+          "value": "We are on GitHub",
+          "href": "https://github.com/w3c/wot-discovery/"
+        },
+        {
+          "value": "File a bug",
+          "href": "https://github.com/w3c/wot-discovery/issues"
+        }
+      ]
+    }
+  ],
+  "localBiblio": {
+    "Discovery-Categorization-IoT": {
+      "title": "A Categorization of Discovery Technologies for the Internet of Things",
+      "href": "https://dl.acm.org/doi/10.1145/2991561.2991570",
+      "authors": [
+        "Arne Broering",
+        "Soumya Kanti Datta",
+        "Christian Bonnet"
+      ],
+      "date": "7-9 November 2016",
+      "publisher": "Association of Computing Machinery (ACM): IoT'16 Proceedings",
+      "id": "discovery-categorization-iot"
+    },
+    "GDPR-Defs": {
+      "title": "General Data Protection Regulation (GDPR) Article 4 - Definitions",
+      "href": "https://gdpr-info.eu/art-4-gdpr/",
+      "publisher": "European Union (EU) and the European Economic Area (EEA)",
+      "id": "gdpr-defs"
+    },
+    "OWASP-Top-10": {
+      "title": "OWASP Top Ten",
+      "href": "https://owasp.org/www-project-top-ten/",
+      "publisher": "OWASP",
+      "id": "owasp-top-10"
+    },
+    "REST-IOT": {
+      "title": "RESTful Design for Internet of Things Systems",
+      "href": "https://datatracker.ietf.org/doc/html/draft-irtf-t2trg-rest-iot-06",
+      "authors": [
+        "Ari Keranen",
+        "Matthias Kovatsch",
+        "Klaus Hartke"
+      ],
+      "publisher": "IETF",
+      "date": "11 May 2020",
+      "id": "rest-iot"
+    },
+    "JSONPATH": {
+      "title": "JSONPath: Query expressions for JSON",
+      "href": "https://datatracker.ietf.org/doc/html/draft-ietf-jsonpath-base",
+      "authors": [
+        "Stefan Gössner",
+        "Glyn Normington",
+        "Carsten Bormann"
+      ],
+      "publisher": "IETF",
+      "status": "DRAFT",
+      "id": "jsonpath"
+    },
+    "wot-usecases": {
+      "title": "Web of Things (WoT): Use Cases",
+      "href": "https://w3c.github.io/wot-usecases/",
+      "authors": [
+        "Michael Lagally",
+        "Michael McCool",
+        "Ryuichi Matsukura",
+        "Tomoaki Mizushima"
+      ],
+      "publisher": "W3C",
+      "date": "15 October 2020",
+      "status": "Editor's Draft",
+      "id": "wot-usecases"
+    },
+    "AMPLIFICATION-ATTACKS": {
+      "title": "Amplification Attacks Using the Constrained Application Protocol (CoAP)",
+      "href": "https://datatracker.ietf.org/doc/html/draft-irtf-t2trg-amplification-attacks",
+      "authors": [
+        "John Preuß Mattsson",
+        "Göran Selander",
+        "Christian Amsüss"
+      ],
+      "publisher": "IETF",
+      "status": "DRAFT",
+      "id": "amplification-attacks"
+    }
+  },
+  "publishISODate": "2023-12-05T00:00:00.000Z",
+  "generatedSubtitle": "W3C Recommendation 05 December 2023"
+  }
+]]>
+</script>
+<link rel="stylesheet" href=
+"https://www.w3.org/StyleSheets/TR/2021/W3C-REC" />
+<style type='text/css'>
+.diff-old-a {
+  font-size: smaller;
+  color: red;
+}
+
+.diff-new { background-color: yellow; }
+.diff-chg { background-color: lime; }
+.diff-new:before,
+.diff-new:after
+    { content: "\2191" }
+.diff-chg:before, .diff-chg:after
+    { content: "\2195" }
+.diff-old { text-decoration: line-through; background-color: #FBB; }
+.diff-old:before,
+.diff-old:after
+    { content: "\2193" }
+:focus { border: thin red solid}
+</style>
+</head>
+<body class="h-entry toc-inline">
+<div class="head">
+<p class="logos">
+<a class="logo" href= "https://www.w3.org/">
+<img crossorigin="" alt="W3C" height="48" src="https://www.w3.org/StyleSheets/TR/2021/logos/W3C" width= "72" />
+</a>
+</p>
+<h1 id="title" class="title">
+Web
+of
+Things
+(WoT)
+Discovery
+</h1>
+<p id="w3c-state">
+<a href= "https://www.w3.org/standards/types#REC">
+W3C
+Recommendation
+</a>
+<del class="diff-old">30
+November
+</del>
+<time class="dt-published" datetime="2023-12-05">
+<ins class="diff-chg">05
+December
+</ins>
+2023
+</time>
+</p>
+<details open="">
+<summary>
+More
+details
+about
+this
+document
+</summary>
+<dl>
+<dt>
+This
+version:
+</dt>
+<dd>
+<del class="diff-old">https://www.w3.org/TR/2023/REC-wot-discovery-20231130/
+</del>
+<a class="u-url" href= "https://www.w3.org/TR/2023/REC-wot-discovery-20231205/">
+<ins class="diff-chg">https://www.w3.org/TR/2023/REC-wot-discovery-20231205/
+</ins>
+</a>
+</dd>
+<dt>
+Latest
+published
+version:
+</dt>
+<dd>
+<a href= "https://www.w3.org/TR/wot-discovery/">
+https://www.w3.org/TR/wot-discovery/
+</a>
+</dd>
+<dt>
+Latest
+editor's
+draft:
+</dt>
+<dd>
+<a href= "https://w3c.github.io/wot-discovery/">
+https://w3c.github.io/wot-discovery/
+</a>
+</dd>
+<dt>
+History:
+</dt>
+<dd>
+<a href= "https://www.w3.org/standards/history/wot-discovery/">
+https://www.w3.org/standards/history/wot-discovery/
+</a>
+</dd>
+<dd>
+<a href= "https://github.com/w3c/wot-discovery/commits/main">
+Commit
+history
+</a>
+</dd>
+<dt>
+Implementation
+report:
+</dt>
+<dd>
+<a href= "https://w3c.github.io/wot-discovery/testing/report.html">
+https://w3c.github.io/wot-discovery/testing/report.html
+</a>
+</dd>
+<dt>
+Editors:
+</dt>
+<dd class="editor p-author h-card vcard" data-editor-id="115672">
+<span class="p-name fn">
+Andrea
+Cimmino
+</span>
+(
+<a class= "p-org org h-org" href="https://www.upm.es/">
+Universidad
+Politécnica
+de
+Madrid
+</a>
+)
+</dd>
+<dd class="editor p-author h-card vcard" data-editor-id="93137">
+<span class="p-name fn">
+Michael
+McCool
+</span>
+(
+<a class= "p-org org h-org" href="https://www.intel.com/">
+Intel
+Corp.
+</a>
+)
+</dd>
+<dd class="editor p-author h-card vcard" data-editor-id="122520">
+<span class="p-name fn">
+Farshid
+Tavakolizadeh
+</span>
+(
+<span class= "p-org org h-org">
+Invited
+Expert
+</span>
+)
+</dd>
+<dd class="editor p-author h-card vcard" data-editor-id="83488">
+<span class="p-name fn">
+Kunihiko
+Toumura
+</span>
+(
+<a class= "p-org org h-org" href="https://www.hitachi.com/">
+Hitachi,
+Ltd.
+</a>
+)
+</dd>
+<dt>
+Former
+editor:
+</dt>
+<dd class="editor p-author h-card vcard" data-editor-id="122520">
+<span class="p-name fn">
+Farshid
+Tavakolizadeh
+</span>
+(
+<a class= "p-org org h-org" href= "https://www.fraunhofer.de/">
+Fraunhofer-Gesellschaft
+</a>
+)
+-
+Until
+<time datetime="2021-09-30">
+30
+September
+2021
+</time>
+</dd>
+<dt>
+Feedback:
+</dt>
+<dd>
+<a href="https://github.com/w3c/wot-discovery/">
+GitHub
+w3c/wot-discovery
+</a>
+(
+<a href= "https://github.com/w3c/wot-discovery/pulls/">
+pull
+requests
+</a>,
+<a href= "https://github.com/w3c/wot-discovery/issues/new/choose">
+new
+issue
+</a>,
+<a href= "https://github.com/w3c/wot-discovery/issues/">
+open
+issues
+</a>
+)
+</dd>
+<dd>
+<a href= "mailto:public-wot-wg@w3.org?subject=%5Bwot-discovery%5D%20YOUR%20TOPIC%20HERE">
+public-wot-wg@w3.org
+</a>
+with
+subject
+line
+<kbd>
+[wot-discovery]
+<em>
+…
+message
+topic
+…
+</em>
+</kbd>
+(
+<a rel="discussion" href= "https://lists.w3.org/Archives/Public/public-wot-wg">
+archives
+</a>
+)
+</dd>
+<dt>
+Errata:
+</dt>
+<dd>
+<a href= "https://w3c.github.io/wot-discovery/errata.html">
+Errata
+exists
+</a>.
+</dd>
+<dt>
+Contributors
+</dt>
+<dd>
+<a href= "https://github.com/w3c/wot-discovery/graphs/contributors">
+In
+the
+GitHub
+repository
+</a>
+</dd>
+<dt>
+Repository
+</dt>
+<dd>
+<a href="https://github.com/w3c/wot-discovery/">
+We
+are
+on
+GitHub
+</a>
+</dd>
+<dd>
+<a href="https://github.com/w3c/wot-discovery/issues">
+File
+a
+bug
+</a>
+</dd>
+</dl>
+</details>
+<p>
+See
+also
+<a href= "https://www.w3.org/Translations/?technology=wot-discovery">
+<strong>
+translations
+</strong>
+</a>.
+</p>
+<p class="copyright">
+<a href= "https://www.w3.org/policies/#copyright">
+Copyright
+</a>
+©
+2017-2023
+<a href="https://www.w3.org/">
+World
+Wide
+Web
+Consortium
+</a>.
+<abbr title="World Wide Web Consortium">
+W3C
+</abbr>
+<sup>
+®
+</sup>
+<a href= "https://www.w3.org/policies/#Legal_Disclaimer">
+liability
+</a>,
+<a href="https://www.w3.org/policies/#W3C_Trademarks">
+trademark
+</a>
+and
+<a rel="license" href= "https://www.w3.org/copyright/software-license-2023/" title= "W3C Software and Document Notice and License">
+permissive
+document
+license
+</a>
+rules
+apply.
+</p>
+<hr title="Separator for header" />
+</div>
+<section id="abstract" class="introductory">
+<h2>
+Abstract
+</h2>
+<p>
+The
+<abbr title="World Wide Web Consortium">
+W3C
+</abbr>
+Web
+of
+Things
+(WoT)
+is
+intended
+to
+enable
+interoperability
+across
+IoT
+platforms
+and
+application
+domains.
+One
+key
+mechanism
+for
+accomplishing
+this
+goal
+is
+the
+definition
+and
+use
+of
+metadata
+describing
+the
+interactions
+an
+IoT
+device
+or
+service
+makes
+available
+over
+the
+network
+at
+a
+suitable
+level
+of
+abstraction.
+The
+WoT
+Thing
+Description
+specification
+satisfies
+this
+objective.
+</p>
+<p>
+However,
+in
+order
+to
+use
+a
+Thing
+its
+Thing
+Description
+first
+has
+to
+be
+obtained.
+The
+<em>
+WoT
+Discovery
+</em>
+process
+described
+in
+this
+document
+addresses
+this
+problem.
+WoT
+Discovery
+needs
+to
+support
+the
+distribution
+of
+WoT
+Thing
+Descriptions
+in
+a
+variety
+of
+use
+cases.
+This
+includes
+ad-hoc
+and
+engineered
+systems;
+during
+development
+and
+at
+runtime;
+and
+on
+both
+local
+and
+global
+networks.
+The
+process
+also
+needs
+to
+work
+with
+existing
+discovery
+mechanisms,
+be
+secure,
+protect
+private
+information,
+and
+be
+able
+to
+efficiently
+handle
+updates
+to
+WoT
+Thing
+Descriptions
+and
+the
+dynamic
+and
+diverse
+nature
+of
+the
+IoT
+ecosystem.
+</p>
+<p>
+The
+WoT
+Discovery
+process
+is
+divided
+into
+two
+phases,
+Introduction,
+and
+Exploration.
+The
+Introduction
+phase
+leverages
+existing
+discovery
+mechanisms
+but
+does
+not
+directly
+expose
+metadata;
+they
+are
+simply
+used
+to
+discover
+Exploration
+services,
+which
+provide
+metadata
+but
+only
+after
+secure
+authentication
+and
+authorization.
+This
+document
+normatively
+defines
+two
+Exploration
+services:
+for
+distributing
+a
+single
+WoT
+Thing
+Description
+from
+a
+regular
+web
+service,
+including
+as
+a
+special
+case
+self-description;
+and
+a
+searchable
+WoT
+Thing
+Description
+Directory
+service
+for
+collections
+of
+Thing
+Descriptions.
+A
+variety
+of
+Introduction
+services
+are
+also
+described
+and
+where
+necessary
+normative
+definitions
+are
+given
+to
+support
+them.
+</p>
+</section>
+<section id="sotd" class="introductory">
+<h2>
+Status
+of
+This
+Document
+</h2>
+<p>
+<em>
+This
+section
+describes
+the
+status
+of
+this
+document
+at
+the
+time
+of
+its
+publication.
+A
+list
+of
+current
+<abbr title= "World Wide Web Consortium">
+W3C
+</abbr>
+publications
+and
+the
+latest
+revision
+of
+this
+technical
+report
+can
+be
+found
+in
+the
+<a href= "https://www.w3.org/TR/">
+<abbr title= "World Wide Web Consortium">
+W3C
+</abbr>
+technical
+reports
+index
+</a>
+at
+https://www.w3.org/TR/.
+</em>
+</p>
+<p>
+Future
+updates
+to
+this
+specification
+may
+incorporate
+<a href= "https://www.w3.org/2021/Process-20211102/#allow-new-features">
+new
+features
+</a>.
+</p>
+<p>
+This
+document
+was
+published
+by
+the
+<a href= "https://www.w3.org/groups/wg/wot">
+Web
+of
+Things
+Working
+Group
+</a>
+as
+a
+Recommendation
+using
+the
+<a href= "https://www.w3.org/2023/Process-20231103/#recs-and-notes">
+Recommendation
+track
+</a>.
+</p>
+<p>
+<abbr title="World Wide Web Consortium">
+W3C
+</abbr>
+recommends
+the
+wide
+deployment
+of
+this
+specification
+as
+a
+standard
+for
+the
+Web.
+</p>
+<p>
+A
+<abbr title="World Wide Web Consortium">
+W3C
+</abbr>
+Recommendation
+is
+a
+specification
+that,
+after
+extensive
+consensus-building,
+is
+endorsed
+by
+<abbr title= "World Wide Web Consortium">
+W3C
+</abbr>
+and
+its
+Members,
+and
+has
+commitments
+from
+Working
+Group
+members
+to
+<a href= "https://www.w3.org/Consortium/Patent-Policy/#sec-Requirements">
+royalty-free
+licensing
+</a>
+for
+implementations.
+</p>
+<p>
+This
+document
+was
+produced
+by
+a
+group
+operating
+under
+the
+<a href="https://www.w3.org/Consortium/Patent-Policy/">
+<abbr title= "World Wide Web Consortium">
+W3C
+</abbr>
+Patent
+Policy
+</a>.
+<abbr title="World Wide Web Consortium">
+W3C
+</abbr>
+maintains
+a
+<a rel="disclosure" href= "https://www.w3.org/groups/wg/wot/ipr">
+public
+list
+of
+any
+patent
+disclosures
+</a>
+made
+in
+connection
+with
+the
+deliverables
+of
+the
+group;
+that
+page
+also
+includes
+instructions
+for
+disclosing
+a
+patent.
+An
+individual
+who
+has
+actual
+knowledge
+of
+a
+patent
+which
+the
+individual
+believes
+contains
+<a href= "https://www.w3.org/Consortium/Patent-Policy/#def-essential">
+Essential
+Claim(s)
+</a>
+must
+disclose
+the
+information
+in
+accordance
+with
+<a href= "https://www.w3.org/Consortium/Patent-Policy/#sec-Disclosure">
+section
+6
+of
+the
+<abbr title="World Wide Web Consortium">
+W3C
+</abbr>
+Patent
+Policy
+</a>.
+</p>
+<p>
+This
+document
+is
+governed
+by
+the
+<a id="w3c_process_revision" href="https://www.w3.org/2023/Process-20231103/">
+03
+November
+2023
+<abbr title="World Wide Web Consortium">
+W3C
+</abbr>
+Process
+Document
+</a>.
+</p>
+</section>
+<nav id="toc">
+<h2 class="introductory" id="table-of-contents">
+Table
+of
+Contents
+</h2>
+<ol class="toc">
+<li class="tocline">
+<a class="tocxref" href= "#abstract">
+Abstract
+</a>
+</li>
+<li class="tocline">
+<a class="tocxref" href="#sotd">
+Status
+of
+This
+Document
+</a>
+</li>
+<li class="tocline">
+<a class="tocxref" href= "#introduction">
+<bdi class="secno">
+1.
+</bdi>
+Introduction
+</a>
+</li>
+<li class="tocline">
+<a class="tocxref" href= "#conformance">
+<bdi class="secno">
+2.
+</bdi>
+Conformance
+</a>
+</li>
+<li class="tocline">
+<a class="tocxref" href= "#terminology">
+<bdi class="secno">
+3.
+</bdi>
+Terminology
+</a>
+</li>
+<li class="tocline">
+<a class="tocxref" href= "#architecture">
+<bdi class="secno">
+4.
+</bdi>
+Architecture
+</a>
+</li>
+<li class="tocline">
+<a class="tocxref" href= "#discoverer-process">
+<bdi class="secno">
+5.
+</bdi>
+Discoverer
+Process
+</a>
+</li>
+<li class="tocline">
+<a class="tocxref" href= "#introduction-mech">
+<bdi class="secno">
+6.
+</bdi>
+Introduction
+Mechanisms
+</a>
+<ol class="toc">
+<li class="tocline">
+<a class="tocxref" href= "#introduction-direct">
+<bdi class="secno">
+6.1
+</bdi>
+Direct
+</a>
+</li>
+<li class="tocline">
+<a class="tocxref" href= "#introduction-well-known">
+<bdi class="secno">
+6.2
+</bdi>
+Well-Known
+URIs
+</a>
+</li>
+<li class="tocline">
+<a class="tocxref" href= "#introduction-dns-sd-sec">
+<bdi class="secno">
+6.3
+</bdi>
+DNS-Based
+Service
+Discovery
+</a>
+</li>
+<li class="tocline">
+<a class="tocxref" href= "#introduction-core-rd-sec">
+<bdi class="secno">
+6.4
+</bdi>
+CoRE
+Link
+Format
+and
+CoRE
+Resource
+Directory
+</a>
+</li>
+<li class="tocline">
+<a class="tocxref" href= "#introduction-did-sec">
+<bdi class="secno">
+6.5
+</bdi>
+DID
+Documents
+</a>
+</li>
+</ol>
+</li>
+<li class="tocline">
+<a class="tocxref" href= "#exploration-mech">
+<bdi class="secno">
+7.
+</bdi>
+Exploration
+Mechanisms
+</a>
+<ol class="toc">
+<li class="tocline">
+<a class="tocxref" href= "#exploration-overview">
+<bdi class="secno">
+7.1
+</bdi>
+Overview
+</a>
+<ol class="toc">
+<li class="tocline">
+<a class="tocxref" href= "#exploration-ontology">
+<bdi class="secno">
+7.1.1
+</bdi>
+Ontology
+</a>
+<ol class="toc">
+<li class="tocline">
+<a class="tocxref" href= "#exploration-td-type-thingdirectory">
+<bdi class= "secno">
+7.1.1.1
+</bdi>
+<code>
+ThingDirectory
+</code>
+</a>
+</li>
+<li class="tocline">
+<a class="tocxref" href= "#exploration-td-type-thinglink">
+<bdi class="secno">
+7.1.1.2
+</bdi>
+<code>
+ThingLink
+</code>
+</a>
+</li>
+</ol>
+</li>
+<li class="tocline">
+<a class="tocxref" href= "#exploration-secboot">
+<bdi class="secno">
+7.1.2
+</bdi>
+Security
+Bootstrapping
+</a>
+</li>
+</ol>
+</li>
+<li class="tocline">
+<a class="tocxref" href= "#exploration-server">
+<bdi class="secno">
+7.2
+</bdi>
+Thing
+Description
+Server
+</a>
+</li>
+<li class="tocline">
+<a class="tocxref" href= "#exploration-directory">
+<bdi class="secno">
+7.3
+</bdi>
+Thing
+Description
+Directory
+</a>
+<ol class="toc">
+<li class="tocline">
+<a class="tocxref" href= "#exploration-directory-info">
+<bdi class="secno">
+7.3.1
+</bdi>
+Information
+Model
+</a>
+<ol class="toc">
+<li class="tocline">
+<a class="tocxref" href= "#exploration-directory-registration-info">
+<bdi class= "secno">
+7.3.1.1
+</bdi>
+Registration
+Information
+</a>
+</li>
+<li class="tocline">
+<a class="tocxref" href= "#exploration-directory-registration-expiry">
+<bdi class= "secno">
+7.3.1.2
+</bdi>
+Registration
+Expiry
+</a>
+</li>
+<li class="tocline">
+<a class="tocxref" href= "#exploration-directory-anonymous-td">
+<bdi class= "secno">
+7.3.1.3
+</bdi>
+Anonymous
+TD
+Identifiers
+</a>
+</li>
+</ol>
+</li>
+<li class="tocline">
+<a class="tocxref" href= "#exploration-directory-api">
+<bdi class="secno">
+7.3.2
+</bdi>
+Directory
+Service
+API
+</a>
+<ol class="toc">
+<li class="tocline">
+<a class="tocxref" href= "#exploration-directory-api-things">
+<bdi class= "secno">
+7.3.2.1
+</bdi>
+Things
+API
+</a>
+<ol class="toc">
+<li class="tocline">
+<a class="tocxref" href= "#exploration-directory-api-things-creation">
+<bdi class= "secno">
+7.3.2.1.1
+</bdi>
+Creation
+</a>
+</li>
+<li class="tocline">
+<a class="tocxref" href= "#exploration-directory-api-things-retrieval">
+<bdi class= "secno">
+7.3.2.1.2
+</bdi>
+Retrieval
+</a>
+</li>
+<li class="tocline">
+<a class="tocxref" href= "#exploration-directory-api-things-update">
+<bdi class= "secno">
+7.3.2.1.3
+</bdi>
+Update
+</a>
+</li>
+<li class="tocline">
+<a class="tocxref" href= "#exploration-directory-api-things-deletion">
+<bdi class= "secno">
+7.3.2.1.4
+</bdi>
+Deletion
+</a>
+</li>
+<li class="tocline">
+<a class="tocxref" href= "#exploration-directory-api-things-listing">
+<bdi class= "secno">
+7.3.2.1.5
+</bdi>
+Listing
+</a>
+</li>
+<li class="tocline">
+<a class="tocxref" href= "#exploration-directory-api-things-validation">
+<bdi class= "secno">
+7.3.2.1.6
+</bdi>
+Validation
+</a>
+</li>
+</ol>
+</li>
+<li class="tocline">
+<a class="tocxref" href= "#exploration-directory-api-notification">
+<bdi class= "secno">
+7.3.2.2
+</bdi>
+Events
+API
+</a>
+</li>
+<li class="tocline">
+<a class="tocxref" href= "#exploration-directory-api-search">
+<bdi class= "secno">
+7.3.2.3
+</bdi>
+Search
+API
+</a>
+<ol class="toc">
+<li class="tocline">
+<a class="tocxref" href= "#jsonpath-semantic">
+<bdi class="secno">
+7.3.2.3.1
+</bdi>
+Syntactic
+search:
+JSONPath
+</a>
+</li>
+<li class="tocline">
+<a class="tocxref" href= "#xpath-semantic">
+<bdi class="secno">
+7.3.2.3.2
+</bdi>
+Syntactic
+search:
+XPath
+</a>
+</li>
+<li class="tocline">
+<a class="tocxref" href= "#search-semantic">
+<bdi class="secno">
+7.3.2.3.3
+</bdi>
+Semantic
+search:
+SPARQL
+</a>
+</li>
+</ol>
+</li>
+<li class="tocline">
+<a class="tocxref" href= "#directory-api-spec">
+<bdi class="secno">
+7.3.2.4
+</bdi>
+API
+Specification
+(Thing
+Model)
+</a>
+</li>
+</ol>
+</li>
+</ol>
+</li>
+</ol>
+</li>
+<li class="tocline">
+<a class="tocxref" href= "#security-considerations">
+<bdi class="secno">
+8.
+</bdi>
+Security
+Considerations
+</a>
+<ol class="toc">
+<li class="tocline">
+<a class="tocxref" href= "#security-consideration-dos">
+<bdi class="secno">
+8.1
+</bdi>
+Denial
+of
+Service
+</a>
+</li>
+<li class="tocline">
+<a class="tocxref" href= "#security-consideration-amp-ddos">
+<bdi class="secno">
+8.2
+</bdi>
+Amplification
+and
+Distributed
+Denial
+of
+Service
+</a>
+</li>
+<li class="tocline">
+<a class="tocxref" href= "#security-consideration-lan-self-discovery">
+<bdi class= "secno">
+8.3
+</bdi>
+Self-Discovery
+on
+LANs
+</a>
+</li>
+</ol>
+</li>
+<li class="tocline">
+<a class="tocxref" href= "#privacy-considerations">
+<bdi class="secno">
+9.
+</bdi>
+Privacy
+Considerations
+</a>
+<ol class="toc">
+<li class="tocline">
+<a class="tocxref" href= "#privacy-consideration-location-tracking">
+<bdi class= "secno">
+9.1
+</bdi>
+Location
+Tracking
+and
+Profiling
+</a>
+</li>
+<li class="tocline">
+<a class="tocxref" href= "#privacy-consideration-query-tracking">
+<bdi class= "secno">
+9.2
+</bdi>
+Query
+Tracking
+</a>
+</li>
+</ol>
+</li>
+<li class="tocline">
+<a class="tocxref" href= "#performance-considerations">
+<bdi class="secno">
+10.
+</bdi>
+Performance
+Considerations
+</a>
+<ol class="toc">
+<li class="tocline">
+<a class="tocxref" href= "#perf-incremental-transfer">
+<bdi class="secno">
+10.1
+</bdi>
+Incremental
+Transfer
+</a>
+</li>
+</ol>
+</li>
+<li class="tocline">
+<a class="tocxref" href= "#iana-considerations">
+<bdi class="secno">
+11.
+</bdi>
+IANA
+Considerations
+</a>
+<ol class="toc">
+<li class="tocline">
+<a class="tocxref" href= "#well-known-uri-suffix">
+<bdi class="secno">
+11.1
+</bdi>
+Well-Known
+URI
+Registration
+</a>
+</li>
+<li class="tocline">
+<a class="tocxref" href= "#service-name">
+<bdi class="secno">
+11.2
+</bdi>
+Service
+Name
+Registration
+</a>
+</li>
+<li class="tocline">
+<a class="tocxref" href= "#core-resource-type">
+<bdi class="secno">
+11.3
+</bdi>
+CoRE
+Resource
+Types
+Registration
+</a>
+</li>
+</ol>
+</li>
+<li class="tocline">
+<a class="tocxref" href= "#other-name-considerations">
+<bdi class="secno">
+12.
+</bdi>
+Other
+Name
+Registration
+Considerations
+</a>
+<ol class="toc">
+<li class="tocline">
+<a class="tocxref" href= "#did-service-name">
+<bdi class="secno">
+12.1
+</bdi>
+DID
+Service
+Name
+Registration
+</a>
+</li>
+</ol>
+</li>
+<li class="tocline">
+<a class="tocxref" href= "#tdd-extensions-jsonschema">
+<bdi class="secno">
+A.
+</bdi>
+JSON
+Schema
+for
+WoT
+Discovery
+TD-extensions
+</a>
+</li>
+<li class="tocline">
+<a class="tocxref" href="#changes">
+<bdi class= "secno">
+B.
+</bdi>
+Recent
+Specification
+Changes
+</a>
+<ol class="toc">
+<li class="tocline">
+<a class="tocxref" href= "#changes-from-pr">
+<bdi class="secno">
+B.1
+</bdi>
+Changes
+from
+11
+July
+2023
+Proposed
+Recommendation
+</a>
+</li>
+<li class="tocline">
+<a class="tocxref" href= "#changes-from-cr">
+<bdi class="secno">
+B.2
+</bdi>
+Changes
+from
+19
+January
+2023
+Candidate
+Recommendation
+</a>
+</li>
+<li class="tocline">
+<a class="tocxref" href= "#changes-from-third-draft">
+<bdi class="secno">
+B.3
+</bdi>
+Changes
+from
+10
+August
+2022
+Working
+Draft
+</a>
+</li>
+<li class="tocline">
+<a class="tocxref" href= "#changes-from-second-draft">
+<bdi class="secno">
+B.4
+</bdi>
+Changes
+from
+2
+June
+2021
+Working
+Draft
+</a>
+</li>
+<li class="tocline">
+<a class="tocxref" href= "#changes-from-first-draft">
+<bdi class="secno">
+B.5
+</bdi>
+Changes
+from
+24
+November
+2020
+First
+Public
+Working
+Draft
+</a>
+</li>
+</ol>
+</li>
+<li class="tocline">
+<a class="tocxref" href= "#acknowledgements">
+<bdi class="secno">
+C.
+</bdi>
+Acknowledgments
+</a>
+</li>
+<li class="tocline">
+<a class="tocxref" href= "#references">
+<bdi class="secno">
+D.
+</bdi>
+References
+</a>
+<ol class="toc">
+<li class="tocline">
+<a class="tocxref" href= "#normative-references">
+<bdi class="secno">
+D.1
+</bdi>
+Normative
+references
+</a>
+</li>
+<li class="tocline">
+<a class="tocxref" href= "#informative-references">
+<bdi class="secno">
+D.2
+</bdi>
+Informative
+references
+</a>
+</li>
+</ol>
+</li>
+</ol>
+</nav>
+<section id="introduction">
+<div class="header-wrapper">
+<h2 id="x1-introduction">
+<bdi class="secno">
+1.
+</bdi>
+Introduction
+</h2>
+<a class="self-link" href="#introduction" aria-label= "Permalink for Section 1.">
+</a>
+</div>
+<p>
+The
+Web
+of
+Things
+(WoT)
+defines
+an
+architecture
+that
+supports
+the
+integration
+and
+use
+of
+web
+technologies
+with
+IoT
+devices.
+The
+WoT
+Architecture
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href="#bib-wot-architecture11" title= "Web of Things (WoT) Architecture 1.1">
+wot-architecture11
+</a>
+</cite>
+]
+document
+defines
+the
+basic
+concepts
+and
+patterns
+of
+usage
+supported.
+However,
+the
+WoT
+Thing
+Description
+[
+<cite>
+<a class= "bibref" data-link-type="biblio" href= "#bib-wot-thing-description11" title= "Web of Things (WoT) Thing Description 1.1">
+wot-thing-description11
+</a>
+</cite>
+]
+is
+a
+key
+specification
+for
+WoT
+Discovery
+since
+it
+is
+the
+purpose
+of
+WoT
+Discovery
+to
+make
+WoT
+Thing
+Descriptions
+available.
+Specifically,
+WoT
+Discovery
+has
+to
+allow
+authenticated
+and
+authorized
+entities
+(and
+only
+those
+entities)
+to
+find
+WoT
+Thing
+Descriptions
+satisfying
+a
+set
+of
+criteria,
+such
+as
+having
+certain
+semantics,
+or
+containing
+certain
+interactions.
+Conversely,
+in
+order
+to
+support
+security
+and
+privacy
+objectives,
+the
+WoT
+Discovery
+process
+must
+not
+leak
+information
+to
+unauthorized
+entities.
+This
+includes
+leaking
+information
+that
+a
+given
+entity
+is
+requesting
+certain
+information,
+not
+just
+the
+information
+distributed
+in
+the
+Thing
+Descriptions
+themselves.
+</p>
+<p>
+There
+are
+already
+a
+number
+of
+discovery
+mechanisms
+defined
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href= "#bib-discovery-categorization-iot" title= "A Categorization of Discovery Technologies for the Internet of Things">
+Discovery-Categorization-IoT
+</a>
+</cite>
+],
+so
+we
+have
+to
+establish
+why
+we
+are
+proposing
+a
+new
+one.
+First,
+many
+existing
+discovery
+mechanisms
+have
+relatively
+weak
+security
+and
+privacy
+protections.
+One
+of
+our
+objectives
+is
+to
+establish
+a
+mechanism
+that
+not
+only
+uses
+best
+practices
+to
+protect
+metadata,
+but
+that
+can
+be
+upgraded
+to
+support
+future
+best
+practices
+as
+needed.
+Second,
+we
+are
+using
+discovery
+in
+a
+broad
+sense
+to
+include
+both
+local
+and
+non-local
+mechanisms.
+While
+a
+local
+mechanism
+might
+use
+a
+broadcast
+protocol,
+non-local
+mechanisms
+might
+go
+beyond
+the
+current
+network
+segment
+where
+broadcast
+is
+not
+scalable,
+and
+so
+a
+different
+approach,
+such
+as
+a
+search
+service,
+is
+needed.
+Our
+approach
+is
+to
+use
+existing
+mechanisms
+as
+needed
+to
+bootstrap
+into
+a
+more
+general
+and
+secure
+metadata
+distribution
+system.
+Third,
+the
+metadata
+we
+are
+distributing,
+the
+WoT
+Thing
+Description,
+is
+highly
+structured
+and
+includes
+rich
+data
+such
+as
+data
+schemas
+and
+semantic
+annotations.
+Existing
+discovery
+mechanisms
+based
+on
+a
+list
+of
+simple
+key-value
+pairs
+are
+not
+appropriate.
+At
+the
+same
+time,
+use
+of
+existing
+standards
+for
+semantic
+data
+query,
+such
+as
+SPARQL
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href= "#bib-sparql11-overview" title= "SPARQL 1.1 Overview">
+SPARQL11-OVERVIEW
+</a>
+</cite>
+],
+while
+potentially
+suitable
+for
+some
+advanced
+use
+cases,
+might
+require
+too
+much
+effort
+for
+many
+anticipated
+IoT
+applications.
+Therefore
+in
+order
+to
+address
+more
+basic
+applications,
+we
+also
+define
+some
+simpler
+query
+mechanisms.
+</p>
+<p>
+After
+defining
+some
+basic
+terminology,
+we
+will
+summarize
+the
+basic
+use
+cases
+and
+requirements
+for
+WoT
+Discovery.
+These
+are
+a
+subset
+of
+the
+more
+detailed
+and
+exhaustive
+use
+cases
+and
+requirements
+presented
+in
+the
+WoT
+Use
+Cases
+[
+<cite>
+<a class= "bibref" data-link-type="biblio" href="#bib-wot-usecases" title= "Web of Things (WoT): Use Cases">
+wot-usecases
+</a>
+</cite>
+]
+and
+WoT
+Architecture
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href= "#bib-wot-architecture11" title= "Web of Things (WoT) Architecture 1.1">
+wot-architecture11
+</a>
+</cite>
+]
+documents.
+Then
+we
+will
+describe
+the
+basic
+architecture
+of
+the
+WoT
+Discovery
+process,
+which
+uses
+a
+two-phase
+Introduction/Exploration
+approach.
+The
+basic
+goal
+of
+this
+architecture
+is
+to
+be
+able
+to
+use
+existing
+discovery
+standards
+to
+bootstrap
+access
+to
+protected
+discovery
+services,
+but
+to
+distribute
+detailed
+metadata
+only
+to
+authorized
+users,
+and
+to
+also
+protect
+those
+making
+queries
+from
+eavesdroppers
+as
+much
+as
+possible.
+We
+then
+describe
+details
+of
+specific
+Introduction
+and
+Exploration
+mechanisms.
+In
+particular,
+we
+define
+in
+detail
+a
+normative
+API
+for
+a
+WoT
+Thing
+Description
+Directory
+(WoT
+TDD)
+service
+that
+provides
+a
+search
+mechanism
+for
+collections
+of
+WoT
+Thing
+Descriptions
+that
+can
+be
+dynamically
+registered
+by
+Things
+or
+entities
+acting
+on
+their
+behalf.
+The
+WoT
+Discovery
+mechanism
+however
+also
+supports
+distribution
+of
+single
+TDs
+from
+regular
+web
+services,
+with
+a
+special
+case
+of
+this
+being
+self-description.
+Finally,
+we
+discuss
+some
+security
+and
+privacy
+considerations,
+including
+a
+set
+of
+potential
+risks
+and
+mitigations.
+</p>
+</section>
+<section id="conformance">
+<div class="header-wrapper">
+<h2 id="x2-conformance">
+<bdi class="secno">
+2.
+</bdi>
+Conformance
+</h2>
+<a class="self-link" href="#conformance" aria-label= "Permalink for Section 2.">
+</a>
+</div>
+<p>
+As
+well
+as
+sections
+marked
+as
+non-normative,
+all
+authoring
+guidelines,
+diagrams,
+examples,
+and
+notes
+in
+this
+specification
+are
+non-normative.
+Everything
+else
+in
+this
+specification
+is
+normative.
+</p>
+<p>
+The
+key
+words
+<em class="rfc2119">
+MAY
+</em>,
+<em class= "rfc2119">
+MUST
+</em>,
+<em class="rfc2119">
+OPTIONAL
+</em>,
+<em class= "rfc2119">
+RECOMMENDED
+</em>,
+<em class="rfc2119">
+SHOULD
+</em>,
+and
+<em class="rfc2119">
+SHOULD
+NOT
+</em>
+in
+this
+document
+are
+to
+be
+interpreted
+as
+described
+in
+<a href= "https://datatracker.ietf.org/doc/html/bcp14">
+BCP
+14
+</a>
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href= "#bib-rfc2119" title= "Key words for use in RFCs to Indicate Requirement Levels">
+RFC2119
+</a>
+</cite>
+]
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href= "#bib-rfc8174" title= "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words">
+RFC8174
+</a>
+</cite>
+]
+when,
+and
+only
+when,
+they
+appear
+in
+all
+capitals,
+as
+shown
+here.
+</p>
+</section>
+<section id="terminology" class="informative">
+<div class="header-wrapper">
+<h2 id="x3-terminology">
+<bdi class="secno">
+3.
+</bdi>
+Terminology
+</h2>
+<a class="self-link" href="#terminology" aria-label= "Permalink for Section 3.">
+</a>
+</div>
+<p>
+<em>
+This
+section
+is
+non-normative.
+</em>
+</p>
+<p>
+The
+fundamental
+WoT
+terminology
+such
+as
+<dfn id="dfn-thing" tabindex="0" aria-haspopup="dialog" data-dfn-type= "dfn">
+Thing
+</dfn>,
+<dfn data-plurals="thing descriptions" id= "dfn-thing-description" tabindex="0" aria-haspopup="dialog" data-dfn-type="dfn">
+Thing
+Description
+</dfn>
+(
+<dfn data-plurals= "tds" id="dfn-td" tabindex="0" aria-haspopup="dialog" data-dfn-type="dfn">
+TD
+</dfn>
+),
+<dfn id="dfn-thing-model" tabindex= "0" aria-haspopup="dialog" data-dfn-type="dfn">
+Thing
+Model
+</dfn>
+(
+<dfn id="dfn-tm" tabindex="0" aria-haspopup="dialog" data-dfn-type="dfn">
+TM
+</dfn>
+),
+<dfn id="dfn-property" tabindex="0" aria-haspopup="dialog" data-dfn-type="dfn">
+Property
+</dfn>,
+<dfn id= "dfn-action" tabindex="0" aria-haspopup="dialog" data-dfn-type= "dfn">
+Action
+</dfn>,
+<dfn id="dfn-event" tabindex="0" aria-haspopup= "dialog" data-dfn-type="dfn">
+Event
+</dfn>,
+<dfn data-lt= "WoT Anonymous Thing Description|Anonymous TD" data-plurals= "anonymous tds" id="dfn-wot-anonymous-thing-description" tabindex= "0" aria-haspopup="dialog" data-dfn-type="dfn">
+Anonymous
+TD
+</dfn>,
+<dfn data-lt="WoT Discoverer|Discoverer" id="dfn-wot-discoverer" tabindex="0" aria-haspopup="dialog" data-dfn-type= "dfn">
+Discoverer
+</dfn>,
+<dfn data-lt="WoT Discovery|Discovery" id= "dfn-wot-discovery" tabindex="0" aria-haspopup="dialog" data-dfn-type="dfn">
+Discovery
+</dfn>,
+<dfn data-lt= "WoT Exploration|Exploration" id="dfn-wot-exploration" tabindex="0" aria-haspopup="dialog" data-dfn-type="dfn">
+Exploration
+</dfn>,
+<dfn data-lt="WoT Introduction|Introduction" id= "dfn-wot-introduction" tabindex="0" aria-haspopup="dialog" data-dfn-type="dfn">
+Introduction
+</dfn>,
+<dfn data-lt= "WoT Thing Description Server|Thing Description Server" id= "dfn-wot-thing-description-server" tabindex="0" aria-haspopup= "dialog" data-dfn-type="dfn">
+Thing
+Description
+Server
+</dfn>
+(
+<dfn data-lt="WoT TD Server|TD Server" data-plurals="td servers" id="dfn-wot-td-server" tabindex="0" aria-haspopup="dialog" data-dfn-type="dfn">
+TD
+Server
+</dfn>
+),
+<dfn data-lt= "WoT Thing Description Directory|Thing Description Directory" data-plurals="thing description directories" id= "dfn-wot-thing-description-directory" tabindex="0" aria-haspopup= "dialog" data-dfn-type="dfn">
+Thing
+Description
+Directory
+</dfn>
+(
+<dfn data-lt="WoT TDD|TDD" id="dfn-wot-tdd" tabindex="0" aria-haspopup="dialog" data-dfn-type="dfn">
+TDD
+</dfn>
+),
+<dfn data-lt="WoT Partial Thing Description|Partial TD" id= "dfn-wot-partial-thing-description" tabindex="0" aria-haspopup= "dialog" data-dfn-type="dfn">
+Partial
+TD
+</dfn>,
+<dfn data-lt= "WoT Enriched Thing Description|Enriched TD" data-plurals= "enriched tds" id="dfn-wot-enriched-thing-description" tabindex="0" aria-haspopup="dialog" data-dfn-type="dfn">
+Enriched
+TD
+</dfn>
+are
+defined
+in
+<a href= "https://www.w3.org/TR/wot-architecture11/#terminology">
+Section
+3
+</a>
+of
+the
+WoT
+Architecture
+1.1
+specification
+[
+<cite>
+<a class= "bibref" data-link-type="biblio" href="#bib-wot-architecture11" title= "Web of Things (WoT) Architecture 1.1">
+wot-architecture11
+</a>
+</cite>
+].
+</p>
+</section>
+<section id="architecture" class="informative">
+<div class="header-wrapper">
+<h2 id="x4-architecture">
+<bdi class="secno">
+4.
+</bdi>
+Architecture
+</h2>
+<a class="self-link" href="#architecture" aria-label= "Permalink for Section 4.">
+</a>
+</div>
+<p>
+<em>
+This
+section
+is
+non-normative.
+</em>
+</p>
+<p>
+<a href="#discovery-overview" class="fig-ref" title= "Discovery architecture overview. A set of open Introduction mechanisms provides a set of URLs, which point at Exploration services that only provide metadata (TDs) after suitable authentication. Thing Links and Thing Description Directories provide additional flexibility but retrieving further results from these is at the discretion of the application.">
+Figure
+<bdi class="">
+1
+</bdi>
+</a>
+shows
+an
+overview
+of
+the
+WoT
+Discovery
+process.
+Discovery
+uses
+a
+two-phase
+architecture
+to
+resolve
+the
+competing
+requirements
+to
+be
+both
+open
+and
+to
+restrict
+access
+to
+metadata
+to
+authorized
+entities.
+In
+the
+first
+phase,
+one
+or
+more
+of
+a
+set
+of
+relatively
+open
+"Introduction"
+mechanisms
+may
+be
+used
+to
+generate
+a
+set
+of
+candidate
+URLs.
+These
+URLs
+do
+not
+themselves
+contain
+metadata,
+but
+are
+used
+in
+the
+second
+stage
+to
+reference
+"Exploration"
+services
+that
+can
+actually
+provide
+metadata,
+after
+authentication,
+in
+the
+form
+of
+<a href= "#dfn-thing-description" class="internalDFN" data-link-type="dfn" id="ref-for-dfn-thing-description-1">
+Thing
+Descriptions
+</a>.
+</p>
+<figure id="discovery-overview">
+<img src="images/overview.png" srcset="images/overview.svg" class="wot-diagram" alt= "Discovery process overview" />
+<figcaption>
+<a class="self-link" href="#discovery-overview">
+Figure
+<bdi class="figno">
+1
+</bdi>
+</a>
+<span class="fig-title">
+Discovery
+architecture
+overview.
+A
+set
+of
+open
+Introduction
+mechanisms
+provides
+a
+set
+of
+URLs,
+which
+point
+at
+Exploration
+services
+that
+only
+provide
+metadata
+(TDs)
+after
+suitable
+authentication.
+Thing
+Links
+and
+Thing
+Description
+Directories
+provide
+additional
+flexibility
+but
+retrieving
+further
+results
+from
+these
+is
+at
+the
+discretion
+of
+the
+application.
+</span>
+</figcaption>
+</figure>
+<p>
+The
+intention
+is
+that
+Introduction
+mechanisms
+are
+relatively
+open
+"first
+contact"
+mechanisms
+to
+provide
+a
+starting
+point
+for
+the
+rest
+of
+the
+Discovery
+process.
+In
+this
+document
+we
+specify
+details
+on
+several
+Introduction
+mechanisms,
+suitable
+for
+different
+use
+cases,
+including
+both
+local
+and
+non-local
+scenarios,
+but
+Introductions
+can
+in
+fact
+be
+provided
+by
+any
+mechanism
+that
+can
+return
+a
+URL.
+Introductions,
+however,
+do
+not
+include
+any
+security
+or
+privacy
+controls
+and
+so
+should
+not
+provide
+metadata
+directly.
+Instead,
+the
+URLs
+provided
+by
+Introduction
+mechanisms
+reference
+"Exploration"
+services.
+Exploration
+services
+actually
+do
+provide
+metadata,
+but
+only
+after
+suitable
+authentication
+and
+access
+controls
+have
+been
+applied.
+</p>
+<p>
+The
+Discovery
+process
+can
+produce
+a
+<em>
+set
+</em>
+of
+URLs
+as
+output
+from
+its
+Introduction
+phase,
+even
+if
+only
+one
+Introduction
+mechanism
+is
+used
+(some
+Introduction
+mechanisms
+can
+themselves
+return
+multiple
+URLs).
+The
+final
+output
+after
+the
+Exploration
+phase
+can
+also
+be
+a
+<em>
+set
+</em>
+of
+Thing
+Descriptions.
+</p>
+<p>
+Each
+URL
+provided
+by
+the
+Introduction
+phase
+always
+points
+at
+an
+Exploration
+service
+endpoint
+that
+will
+return
+a
+single
+Thing
+Description.
+In
+the
+simplest
+case
+this
+URL
+references
+an
+ordinary
+resource
+provided
+by
+a
+web
+server
+which
+provides
+the
+Thing
+Description
+of
+a
+Thing
+describing
+an
+IoT
+endpoint
+device.
+As
+a
+special
+case
+of
+this,
+for
+self-describing
+Things
+an
+Introduction
+URL
+might
+point
+directly
+at
+an
+endpoint
+provided
+by
+a
+Thing
+serving
+its
+own
+Thing
+Description.
+</p>
+<p>
+In
+general
+Thing
+Descriptions
+might
+be
+provided
+in
+various
+ways
+and
+in
+particular
+may
+not
+be
+self-describing.
+For
+example,
+</p>
+<ul>
+<li>
+brownfield
+devices
+not
+designed
+with
+the
+WoT
+specification
+in
+mind
+will
+not
+be
+capable
+of
+serving
+their
+own
+Thing
+Descriptions;
+</li>
+<li>
+battery-powered
+devices
+may
+not
+be
+online
+most
+of
+the
+time;
+and
+</li>
+<li>
+some
+devices
+may
+not
+be
+powerful
+enough
+to
+manage
+and
+serve
+TDs
+directly.
+</li>
+</ul>
+<p>
+The
+Thing
+Description
+for
+such
+Things
+should
+be
+provided
+by
+separate
+services.
+</p>
+<p>
+This
+document
+specifies
+two
+special
+cases
+that
+allow
+for
+more
+flexibility:
+</p>
+<ul>
+<li>
+A
+Thing
+Description
+referenced
+by
+an
+Introduction
+URL
+may
+describe
+a
+<a href="#exploration-td-type-thingdirectory">
+Thing
+Description
+Directory
+</a>
+service.
+A
+Thing
+Description
+Directory
+service
+(which
+is
+still
+a
+Thing)
+maintains
+a
+(possibly
+dynamic)
+database
+of
+Thing
+Descriptions.
+Thing
+Description
+Directories
+that
+maintain
+large
+numbers
+of
+Thing
+Descriptions
+may
+also
+support
+queries
+that
+can
+be
+used
+to
+selectively
+retrieve
+Thing
+Descriptions.
+</li>
+<li>
+The
+second
+special
+case
+is
+a
+<a href= "#exploration-td-type-thinglink">
+Thing
+Link
+</a>.
+A
+Thing
+Link
+is
+also
+a
+Thing
+Description,
+but
+rather
+than
+describing
+a
+Thing
+directly,
+it
+holds
+a
+link
+to
+a
+Thing
+Description
+hosted
+elsewhere.
+A
+Thing
+Description
+Directory
+can
+also
+store
+Thing
+Links
+which
+can
+redirect
+to
+other
+Thing
+Description
+Directories,
+allowing
+for
+a
+linked
+directory
+structure.
+</li>
+</ul>
+<p>
+It
+is
+<em>
+not
+</em>
+mandatory
+for
+the
+Discovery
+process
+to
+retrieve
+the
+contents
+of
+Thing
+Description
+Directories
+and
+return
+them
+as
+part
+of
+the
+results,
+because
+in
+general
+this
+might
+result
+in
+a
+huge
+set
+of
+results.
+Instead
+the
+application
+should
+scan
+the
+results
+for
+Thing
+Description
+Directory
+TDs
+and
+decide
+whether
+to
+retrieve
+TDs
+from
+them,
+possibly
+selectively.
+Likewise,
+it
+is
+not
+required
+to
+follow
+Thing
+Links
+automatically;
+instead
+the
+application
+may
+choose
+to
+follow
+them
+selectively.
+</p>
+</section>
+<section id="discoverer-process" class="normative">
+<div class="header-wrapper">
+<h2 id="x5-discoverer-process">
+<bdi class="secno">
+5.
+</bdi>
+Discoverer
+Process
+</h2>
+<a class="self-link" href="#discoverer-process" aria-label= "Permalink for Section 5.">
+</a>
+</div>
+<p>
+In
+this
+section
+we
+will
+describe
+the
+WoT
+Discovery
+process
+from
+the
+point
+of
+view
+of
+a
+client,
+and
+what
+it
+means
+to
+say
+that
+a
+client
+supports
+WoT
+Discovery.
+We
+will
+use
+the
+term
+<a href= "#dfn-wot-discoverer" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-wot-discoverer-1">
+Discoverer
+</a>
+for
+an
+entity
+that
+is
+a
+client
+of
+the
+WoT
+Discovery
+process.
+A
+Discoverer
+may
+or
+may
+not
+be
+a
+full
+Consumer.
+A
+Discoverer
+does
+however
+need
+to
+read
+and
+extract
+information
+from
+special
+TDs
+for
+Directories
+and
+Thing
+Links
+and
+use
+specific
+affordances
+and
+links
+provided
+in
+them.
+Conversely,
+a
+Consumer
+may
+not
+support
+Discovery,
+although
+it
+is
+recommended
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href= "#bib-wot-architecture11" title= "Web of Things (WoT) Architecture 1.1">
+wot-architecture11
+</a>
+</cite>
+].
+</p>
+<p>
+The
+WoT
+Discovery
+process
+is
+designed
+so
+that
+nearly
+any
+client
+that
+can
+fetch
+a
+single
+TD
+given
+a
+single
+URI
+can
+be
+said
+to
+support
+WoT
+Discovery.
+Of
+course,
+Discoverers
+may
+support
+more
+powerful
+Discovery
+mechanisms,
+but
+some
+of
+these
+have
+additional
+requirements.
+Some
+Introduction
+mechanisms
+can
+return
+multiple
+URLs,
+each
+of
+which
+can
+in
+turn
+be
+used
+to
+fetch
+at
+least
+one
+TD.
+So
+even
+without
+a
+TDD,
+it
+is
+possible
+to
+discover
+multiple
+TDs.
+</p>
+<p>
+The
+following
+assertions
+describe
+the
+specific
+responsibilities
+of
+a
+Discoverer:
+</p>
+<ul>
+<li>
+<span class="rfc2119-assertion" id= "discoverer-must-support-intros">
+A
+Discoverer
+<em class= "rfc2119">
+MUST
+</em>
+support
+at
+least
+one
+Introduction
+mechanism.
+</span>
+The
+simplest
+Introduction
+mechanism,
+Direct,
+simply
+provides
+a
+single
+URL
+of
+a
+target
+TD.
+This
+assertion
+results
+in
+different
+minimal
+requirements
+depending
+on
+which
+Introduction
+mechanism
+is
+selected
+out
+of
+the
+several
+available.
+For
+example,
+when
+Direct
+is
+used
+as
+the
+sole
+Introduction
+mechanism,
+at
+a
+minimum
+a
+Discoverer
+must
+be
+able
+to
+accept
+a
+single
+URL
+pointing
+at
+a
+TD.
+Note,
+however,
+that
+this
+TD
+could
+still
+be
+describing
+a
+Directory.
+Another
+option
+would
+be
+for
+a
+Discoverer
+to
+implement,
+as
+its
+sole
+Introduction
+mechanism,
+an
+"automatic"
+Introduction
+mechanism
+such
+as
+DNS-SD,
+possibly
+in
+combination
+with
+mDNS.
+In
+this
+case
+the
+application
+code
+running
+in
+the
+Discoverer
+would
+not
+have
+to
+supply
+any
+additional
+information
+to
+invoke
+Discovery.
+</li>
+<li>
+<span class="rfc2119-assertion" id= "discoverer-must-support-fetching">
+A
+Discoverer
+<em class= "rfc2119">
+MUST
+</em>
+support
+fetching
+a
+TD
+from
+at
+least
+one
+URL
+provided
+as
+part
+of
+the
+Introduction
+process.
+</span>
+In
+other
+words,
+not
+only
+must
+a
+Discoverer
+accept
+URLs
+pointing
+at
+TDs,
+it
+must
+be
+able
+to
+fetch
+that
+TD,
+for
+example
+by
+using
+a
+GET
+for
+an
+HTTP
+URL.
+It
+is
+permissible
+to
+split
+the
+implementation
+of
+a
+Discoverer
+into
+two
+components,
+one
+that
+fetches/reads
+a
+TD
+and
+sets
+up
+a
+configuration
+during
+installation
+to
+be
+used
+by
+a
+run-time
+component
+that
+cannot
+itself
+read
+TDs.
+In
+this
+case,
+however,
+the
+latter
+component
+is
+not
+by
+itself
+a
+Discoverer.
+</li>
+<li>
+<span class="rfc2119-assertion" id= "discoverer-may-multiple-intro">
+A
+Discoverer
+<em class= "rfc2119">
+MAY
+</em>
+support
+multiple
+invocations
+of
+the
+same
+Introduction
+mechanism.
+</span>
+If
+multiple
+invocations
+of
+a
+single
+Introduction
+mechanism
+is
+supported,
+or
+if
+multiple
+Introduction
+mechanisms
+are
+used,
+then
+the
+Discoverer
+needs
+to
+manage
+a
+set
+of
+Introduction
+results.
+Some
+Introduction
+mechanisms
+themselves
+return
+a
+set
+of
+results,
+e.g.
+CoRE-RD,
+DID,
+or
+DNS-SD.
+Some
+mechanisms,
+such
+as
+scanning
+Bluetooth
+beacons,
+may
+intrinsically
+result
+in
+separate
+multiple
+"invocations".
+However,
+this
+Discoverer
+requirement
+is
+optional
+to
+support
+an
+important
+special
+case:
+it
+is
+permissible
+to
+have
+a
+simple
+Discoverer
+that
+only
+supports
+a
+single
+invocation
+of
+a
+Direct
+Introduction,
+directly
+specifying
+a
+single
+TD
+via
+a
+URL.
+</li>
+<li>
+<span class="rfc2119-assertion" id="discoverer-merge-intros">
+A
+Discoverer
+<em class="rfc2119">
+MUST
+</em>
+be
+able
+to
+merge
+URLs
+resulting
+from
+multiple
+Introduction
+mechanisms,
+multiple
+results
+from
+a
+single
+Introduction
+mechanism,
+and
+multiple
+Introduction
+invocations
+into
+a
+single
+set.
+</span>
+Note
+that
+even
+if
+only
+one
+Introduction
+mechanism
+is
+supported
+multiple
+results
+might
+be
+produced.
+This
+assertion
+states
+that
+the
+overall
+output
+of
+the
+Introduction
+phase
+is
+a
+single
+set
+of
+URLs.
+The
+word
+"set"
+is
+used
+here
+in
+the
+mathematical
+sense:
+the
+results
+are
+unordered
+and
+unique.
+Uniqueness
+means
+that
+if
+multiple
+Introductions
+have
+the
+same
+result,
+they
+are
+merged
+into
+a
+single
+result.
+If
+the
+Discoverer
+only
+supports
+one
+Introduction
+mechanism
+and
+that
+mechanism
+can
+only
+produce
+one
+URL,
+then
+the
+"merge"
+is
+trivial.
+</li>
+<li>
+<span class="rfc2119-assertion" id="discoverer-td-identify">
+A
+Discoverer
+<em class="rfc2119">
+MUST
+</em>
+be
+able
+to
+identify
+whether
+a
+TD
+fetched
+from
+an
+Introduction
+URL
+has
+<a href= "#exploration-td-type-thingdirectory">
+Thing
+Directory
+</a>
+or
+<a href="#exploration-td-type-thingdirectory">
+Thing
+Link
+</a>
+type.
+</span>
+This
+implies
+that
+the
+Discoverer
+needs
+to
+be
+able
+to
+check
+the
+<code>
+@type
+</code>
+field
+and
+make
+this
+distinction.
+A
+Discoverer
+can
+decide
+whether
+or
+not
+to
+follow
+links
+or
+fetch
+TDD
+contents.
+There
+are
+some
+use
+cases
+where
+a
+Consumer
+may
+not
+expand
+certain
+URLs,
+for
+example
+links
+pointing
+at
+external
+resources,
+or
+when
+a
+TDD
+contains
+many
+TDs
+and
+fetching
+them
+all
+would
+exceed
+the
+Consumer's
+memory
+processing
+capabilities.
+</li>
+<li>
+<span class="rfc2119-assertion" id="discoverer-fetch-tdd">
+A
+Discoverer
+<em class="rfc2119">
+MAY
+</em>
+fetch
+additional
+TDs
+from
+any
+Exploration
+mechanism
+described
+in
+its
+initial
+set
+of
+TDs
+(including,
+in
+particular,
+Thing
+Description
+Directories)
+and
+add
+them
+into
+the
+set
+of
+TD
+results.
+</span>
+This
+only
+adds
+the
+results
+of
+fetching
+TDs
+from
+an
+Exploration
+mechanism
+to
+the
+set
+of
+results.
+These
+new
+results
+do
+not
+delete
+the
+original
+TD
+describing
+the
+Exploration
+mechanism.
+A
+Discoverer
+implementation
+can
+decide
+whether
+or
+not
+to
+fetch
+TDD
+contents.
+Implementers
+should
+consider
+the
+fact
+that
+TDDs
+may
+be
+large
+and
+fetching
+the
+contents
+of
+an
+entire
+TDD
+might
+be
+prohibitively
+expensive.
+</li>
+<li>
+<span class="rfc2119-assertion" id="discoverer-fetch-links">
+A
+Discoverer
+<em class="rfc2119">
+MAY
+</em>
+fetch
+source
+TDs
+from
+the
+targets
+of
+the
+links
+in
+a
+<a href= "#exploration-td-type-thingdirectory">
+Thing
+Link
+</a>
+described
+in
+its
+initial
+set
+of
+TDs
+and
+add
+them
+into
+the
+set
+of
+TD
+results.
+</span>
+This
+only
+adds
+the
+results
+of
+fetching
+TDs
+from
+a
+Thing
+Link
+to
+the
+set
+of
+results.
+These
+new
+results
+do
+not
+delete
+the
+original
+TD
+describing
+the
+Thing
+Link.
+A
+Discoverer
+implementation
+can
+decide
+whether
+or
+not
+to
+fetch
+the
+targets
+of
+Thing
+Links.
+</li>
+<li>
+<span class="rfc2119-assertion" id= "discoverer-fetch-iteration">
+A
+Discoverer
+<em class= "rfc2119">
+MAY
+</em>
+fetch
+additional
+TDs
+iteratively
+from
+any
+<a href="#exploration-td-type-thingdirectory">
+Thing
+Link
+</a>
+or
+Exploration
+mechanism
+described
+in
+its
+set
+of
+TDs
+and
+add
+them
+into
+the
+set
+of
+TD
+results.
+</span>
+This
+only
+adds
+the
+results
+of
+fetching
+TDs
+from
+an
+Exploration
+mechanism
+to
+the
+set
+of
+results.
+These
+new
+results
+do
+not
+delete
+the
+original
+TD
+describing
+the
+Exploration
+mechanism.
+</li>
+<li>
+<span class="rfc2119-assertion" id="discoverer-termination">
+A
+Discoverer
+<em class="rfc2119">
+MAY
+</em>
+terminate
+fetching
+additional
+TDs
+at
+any
+point
+or
+for
+any
+reason.
+</span>
+</li>
+<li>
+<span class="rfc2119-assertion" id="discoverer-any-order">
+A
+Discoverer
+<em class="rfc2119">
+MAY
+</em>
+fetch
+additional
+TDs
+by
+following
+links
+or
+fetching
+additional
+TDs
+from
+Exploration
+mechanisms
+(e.g.
+TDDs)
+in
+any
+order.
+</span>
+The
+Discoverer
+can
+fetch
+additional
+TDs
+in
+any
+order
+from
+any
+Exploration
+mechanism
+and
+is
+not
+required
+to
+use
+all
+of
+them.
+</li>
+<li>
+<span class="rfc2119-assertion" id="discoverer-track">
+A
+Discoverer
+<em class="rfc2119">
+MUST
+</em>
+track
+which
+TDs
+describing
+links
+or
+Exploration
+mechanisms
+have
+already
+been
+fetched
+and
+avoid
+fetching
+duplicate
+results.
+</span>
+This
+is
+to
+avoid
+infinite
+loops.
+Note
+that
+Thing
+Description
+Directories
+can
+easily
+refer
+to
+each
+other,
+for
+example,
+so
+fetching
+the
+TDs
+from
+a
+TDD,
+then
+fetching
+all
+those
+TDs
+will
+give
+another
+copy
+of
+the
+original
+TDD's
+TD.
+This
+second
+copy
+should
+NOT
+trigger
+further
+fetches.
+Note
+that
+tracking
+cannot
+depend
+only
+on
+the
+value
+of
+"id"
+fields
+in
+TDs
+since
+this
+field
+is
+optional.
+</li>
+</ul>
+<p>
+The
+above
+process
+supports
+a
+way
+to
+let
+Directories
+reference
+other
+Directories
+without
+duplicating
+their
+TDs:
+a
+Directory
+wanting
+to
+reference
+other
+Directories
+should
+include
+a
+<a href= "#exploration-td-type-thingdirectory">
+Thing
+Link
+</a>
+with
+a
+"describedby"
+relation
+to
+the
+TD
+of
+the
+other
+Directory
+service.
+Then
+the
+above
+process
+would
+expand
+the
+Thing
+Link
+to
+obtain
+the
+actual
+TD
+of
+the
+Directory,
+and
+then
+(optionally)
+use
+the
+appropriate
+Directory
+affordance
+to
+access
+the
+contents
+of
+the
+linked
+Directory.
+Note
+that
+such
+a
+Thing
+Link
+points
+at
+the
+TD
+of
+the
+Directory,
+not
+at
+the
+Directory
+itself.
+These
+may
+or
+may
+not
+be
+hosted
+in
+the
+same
+location.
+</p>
+<p>
+Recursively
+fetching
+the
+contents
+of
+such
+linked
+directories,
+especially
+without
+a
+specific
+query
+or
+filter,
+could
+easily
+result
+in
+downloading
+a
+large
+amount
+of
+data.
+Such
+recursive
+expansion
+should
+be
+limited
+to
+use
+cases
+that
+require
+it,
+such
+as
+inventory,
+auditing,
+or
+indexing.
+</p>
+<p>
+URLs
+for
+Directory
+services
+can
+also
+be
+used
+with
+the
+federation
+capabilities
+of
+SPARQL
+queries,
+noted
+below,
+which
+in
+most
+cases
+will
+be
+a
+more
+efficient
+way
+to
+collect
+specific
+information
+from
+a
+set
+of
+distributed
+directory
+services.
+However,
+SPARQL
+requires
+the
+URL
+of
+a
+SPARQL
+endpoint
+for
+such
+federation,
+which
+can
+be
+found
+in
+the
+TDs
+of
+Directories
+supporting
+SPARQL
+queries.
+This
+is
+not
+the
+same
+as
+the
+URL
+pointing
+at
+the
+TD
+of
+a
+Directory.
+</p>
+</section>
+<section id="introduction-mech" class="normative">
+<div class="header-wrapper">
+<h2 id="x6-introduction-mechanisms">
+<bdi class="secno">
+6.
+</bdi>
+Introduction
+Mechanisms
+</h2>
+<a class="self-link" href="#introduction-mech" aria-label= "Permalink for Section 6.">
+</a>
+</div>
+<p>
+This
+chapter
+describes
+mechanisms
+for
+initial
+contact
+with
+Things
+or
+<a href="#dfn-wot-thing-description-directory" class= "internalDFN" data-link-type="dfn" id= "ref-for-dfn-wot-thing-description-directory-1">
+Thing
+Description
+Directories
+</a>.
+Any
+of
+the
+following
+mechanisms
+may
+be
+provided
+by
+the
+Thing
+or
+the
+<a href="#dfn-wot-thing-description-directory" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-wot-thing-description-directory-2">
+Thing
+Description
+Directory
+</a>
+to
+Consumers.
+The
+result
+of
+an
+introduction
+mechanism
+is
+always
+a
+URL
+(address)
+of
+an
+exploration
+service
+which
+can
+be
+used
+to
+obtain
+detailed
+metadata
+(TDs)
+after
+suitable
+authentication.
+It
+is
+also
+possible
+for
+multiple
+introduction
+mechanisms
+to
+be
+used
+and
+the
+results
+merged.
+No
+particular
+introduction
+mechanism
+is
+mandatory,
+as
+long
+as
+the
+URL
+of
+at
+least
+one
+exploration
+service
+is
+somehow
+obtained.
+</p>
+<section id="introduction-direct" class="normative">
+<div class="header-wrapper">
+<h3 id="x6-1-direct">
+<bdi class="secno">
+6.1
+</bdi>
+Direct
+</h3>
+<a class="self-link" href="#introduction-direct" aria-label= "Permalink for Section 6.1">
+</a>
+</div>
+<p>
+<span class="rfc2119-assertion" id="introduction-direct-url">
+To
+obtain
+an
+URL
+of
+an
+exploration
+service,
+any
+mechanism
+that
+results
+in
+a
+single
+URL
+<em class="rfc2119">
+MAY
+</em>
+be
+used.
+</span>
+This
+includes
+Bluetooth
+beacons,
+QR
+codes,
+and
+written
+URLs
+to
+be
+typed
+by
+a
+user.
+<span class="rfc2119-assertion" id= "introduction-direct-thing-description">
+A
+request
+on
+all
+such
+URLs
+<em class="rfc2119">
+MUST
+</em>
+result
+in
+a
+TD
+as
+prescribed
+in
+<a href="#exploration-mech" data-matched-text= "[[[#exploration-mech]]]" class="sec-ref">
+<bdi class= "secno">
+7.
+</bdi>
+Exploration
+Mechanisms
+</a>.
+</span>
+For
+self-describing
+Things,
+this
+can
+be
+the
+TD
+of
+the
+Thing
+itself.
+<span class="rfc2119-assertion" id= "introduction-direct-directory-description">
+If
+the
+URL
+references
+a
+<a href="#dfn-wot-thing-description-directory" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-wot-thing-description-directory-3">
+Thing
+Description
+Directory
+</a>,
+this
+<em class="rfc2119">
+MUST
+</em>
+be
+the
+Thing
+Description
+of
+the
+<a href="#dfn-wot-thing-description-directory" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-wot-thing-description-directory-4">
+Thing
+Description
+Directory
+</a>.
+</span>
+</p>
+</section>
+<section id="introduction-well-known" class="normative">
+<div class="header-wrapper">
+<h3 id="x6-2-well-known-uris">
+<bdi class="secno">
+6.2
+</bdi>
+Well-Known
+URIs
+</h3>
+<a class="self-link" href="#introduction-well-known" aria-label= "Permalink for Section 6.2">
+</a>
+</div>
+<p>
+<span class="rfc2119-assertion" id= "introduction-well-known-uri">
+A
+Thing
+or
+<a href= "#dfn-wot-thing-description-directory" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-wot-thing-description-directory-5">
+Thing
+Description
+Directory
+</a>
+<em class="rfc2119">
+MAY
+</em>
+use
+the
+Well-Known
+Uniform
+Resource
+Identifier
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href="#bib-rfc8615" title= "Well-Known Uniform Resource Identifiers (URIs)">
+RFC8615
+</a>
+</cite>
+]
+to
+advertise
+its
+presence.
+</span>
+<span class="rfc2119-assertion" id="introduction-well-known-path">
+If
+a
+Thing
+or
+<a href= "#dfn-wot-thing-description-directory" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-wot-thing-description-directory-6">
+Thing
+Description
+Directory
+</a>
+use
+the
+Well-Known
+Uniform
+Resource
+Identifier
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href= "#bib-rfc8615" title= "Well-Known Uniform Resource Identifiers (URIs)">
+RFC8615
+</a>
+</cite>
+]
+to
+advertise
+its
+presence,
+it
+<em class="rfc2119">
+MUST
+</em>
+register
+its
+own
+Thing
+Description
+into
+the
+following
+path:
+<code>
+/.well-known/wot
+</code>.
+</span>
+</p>
+<p>
+<span class="rfc2119-assertion" id= "introduction-well-known-thing-description">
+When
+a
+request
+is
+made
+at
+the
+above
+Well-Known
+URI,
+the
+server
+<em class= "rfc2119">
+MUST
+</em>
+return
+a
+Thing
+Description
+as
+prescribed
+in
+<a href="#exploration-mech" data-matched-text= "[[[#exploration-mech]]]" class="sec-ref">
+<bdi class= "secno">
+7.
+</bdi>
+Exploration
+Mechanisms
+</a>.
+</span>
+</p>
+</section>
+<section id="introduction-dns-sd-sec" class="normative">
+<div class="header-wrapper">
+<h3 id="x6-3-dns-based-service-discovery">
+<bdi class= "secno">
+6.3
+</bdi>
+DNS-Based
+Service
+Discovery
+</h3>
+<a class="self-link" href="#introduction-dns-sd-sec" aria-label= "Permalink for Section 6.3">
+</a>
+</div>
+<p>
+<span class="rfc2119-assertion" id="introduction-dns-sd">
+A
+Thing
+or
+<a href="#dfn-wot-thing-description-directory" class= "internalDFN" data-link-type="dfn" id= "ref-for-dfn-wot-thing-description-directory-7">
+Thing
+Description
+Directory
+</a>
+<em class="rfc2119">
+MAY
+</em>
+use
+DNS-Based
+Service
+Discovery
+(DNS-SD)[
+<cite>
+<a class="bibref" data-link-type="biblio" href="#bib-rfc6763" title= "DNS-Based Service Discovery">
+RFC6763
+</a>
+</cite>
+].
+</span>
+This
+can
+be
+also
+be
+used
+on
+the
+same
+local
+network
+in
+combination
+with
+Multicast
+DNS
+(mDNS)[
+<cite>
+<a class="bibref" data-link-type= "biblio" href="#bib-rfc6762" title= "Multicast DNS">
+RFC6762
+</a>
+</cite>
+].
+</p>
+<p>
+The
+following
+table
+lists
+the
+service
+names
+and
+protocols
+for
+advertising
+their
+presense.
+These
+are
+normative
+since
+each
+has
+a
+valid
+use
+with
+existing
+exploration
+mechanisms:
+</p>
+<table class="def">
+<thead>
+<tr>
+<th>
+Service
+name
+</th>
+<th>
+Thing
+or
+TDD
+</th>
+<th>
+Protocol
+</th>
+</tr>
+</thead>
+<tbody>
+<tr class="rfc2119-table-assertion" id= "introduction-dns-sd-service-name">
+<td>
+<code>
+_wot._tcp
+</code>
+</td>
+<td>
+Thing
+</td>
+<td>
+HTTP
+over
+TCP,
+HTTP
+over
+TLS/TCP,
+CoAP
+over
+TCP,
+or
+CoAP
+over
+TLS/TCP
+</td>
+</tr>
+<tr class="rfc2119-table-assertion" id= "introduction-dns-sd-service-name-directory">
+<td>
+<code>
+_directory._sub._wot._tcp
+</code>
+</td>
+<td>
+TDD
+</td>
+<td>
+HTTP
+over
+TCP,
+HTTP
+over
+TLS/TCP,
+CoAP
+over
+TCP,
+or
+CoAP
+over
+TLS/TCP
+</td>
+</tr>
+<tr class="rfc2119-table-assertion" id= "introduction-dns-sd-service-name-udp">
+<td>
+<code>
+_wot._udp
+</code>
+</td>
+<td>
+Thing
+</td>
+<td>
+CoAP
+over
+UDP
+or
+CoAP
+over
+DTLS/UDP
+</td>
+</tr>
+</tbody>
+</table>
+<p>
+The
+following
+additional
+service
+name
+has
+been
+defined
+for
+future
+use.
+This
+definition
+is
+however
+informative
+since
+there
+is
+currently
+no
+defined
+directory
+service
+using
+CoAP
+over
+UDP:
+</p>
+<table class="def">
+<thead>
+<tr>
+<th>
+Service
+name
+</th>
+<th>
+Thing
+or
+TDD
+</th>
+<th>
+Protocol
+</th>
+</tr>
+</thead>
+<tbody>
+<tr>
+<td>
+<code>
+_directory._sub._wot._udp
+</code>
+</td>
+<td>
+TDD
+</td>
+<td>
+CoAP
+over
+UDP
+or
+CoAP
+over
+DTLS/UDP
+</td>
+</tr>
+</tbody>
+</table>
+<div class="rfc2119-assertion" id="introduction-dns-sd-txt-record">
+<p>
+For
+TCP-based
+services,
+the
+following
+information
+<em class= "rfc2119">
+MUST
+</em>
+be
+included
+in
+the
+<code>
+TXT
+</code>
+record
+that
+is
+pointed
+to
+by
+the
+Service
+Instance
+Name:
+</p>
+<dl>
+<dt>
+<code>
+td
+</code>
+</dt>
+<dd>
+Absolute
+pathname
+of
+the
+Thing
+Description
+of
+the
+Thing
+or
+Thing
+Description
+of
+the
+<a href= "#dfn-wot-thing-description-directory" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-wot-thing-description-directory-8">
+Thing
+Description
+Directory
+</a>.
+</dd>
+<dt>
+<code>
+type
+</code>
+</dt>
+<dd>
+Type
+of
+the
+Thing
+Description,
+i.e.
+<code>
+Thing
+</code>
+or
+<code>
+Directory
+</code>.
+If
+omitted,
+the
+type
+is
+assumed
+to
+be
+<code>
+Thing
+</code>.
+</dd>
+<dt>
+<code>
+scheme
+</code>
+</dt>
+<dd>
+Scheme
+part
+of
+URL.
+One
+of
+the
+following
+values
+can
+be
+specified,
+with
+the
+standard
+registered
+URI
+interpretations
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href= "#bib-rfc7595" title= "Guidelines and Registration Procedures for URI Schemes">
+RFC7595
+</a>
+</cite>
+]:
+<code>
+http
+</code>
+(HTTP
+over
+TCP),
+<code>
+https
+</code>
+(HTTP
+over
+TLS/TCP),
+<code>
+coap+tcp
+</code>
+(CoAP
+over
+TCP),
+or
+<code>
+coaps+tcp
+</code>
+(CoAP
+over
+TLS/TCP).
+If
+omitted,
+the
+scheme
+is
+assumed
+to
+be
+<code>
+http
+</code>.
+</dd>
+</dl>
+</div>
+<div class="rfc2119-assertion" id= "introduction-dns-sd-txt-record-udp">
+<p>
+For
+UDP-based
+services,
+the
+following
+information
+<em class= "rfc2119">
+MUST
+</em>
+be
+included
+in
+the
+<code>
+TXT
+</code>
+record
+that
+is
+pointed
+to
+by
+the
+Service
+Instance
+Name:
+</p>
+<dl>
+<dt>
+<code>
+td
+</code>
+</dt>
+<dd>
+Absolute
+pathname
+of
+the
+Thing
+Description
+of
+the
+Thing
+or
+Thing
+Description
+of
+the
+<a href= "#dfn-wot-thing-description-directory" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-wot-thing-description-directory-9">
+Thing
+Description
+Directory
+</a>.
+</dd>
+<dt>
+<code>
+type
+</code>
+</dt>
+<dd>
+Type
+of
+the
+Thing
+Description,
+i.e.
+<code>
+Thing
+</code>
+or
+<code>
+Directory
+</code>.
+If
+omitted,
+the
+type
+is
+assumed
+to
+be
+<code>
+Thing
+</code>.
+</dd>
+<dt>
+<code>
+scheme
+</code>
+</dt>
+<dd>
+Scheme
+part
+of
+URL.
+One
+of
+the
+following
+values
+can
+be
+specified,
+with
+the
+standard
+registered
+URI
+interpretations
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href= "#bib-rfc7595" title= "Guidelines and Registration Procedures for URI Schemes">
+RFC7595
+</a>
+</cite>
+]:
+<code>
+coap
+</code>
+(CoAP
+over
+UDP)
+or
+<code>
+coaps
+</code>
+(CoAP
+over
+DTLS/UDP).
+If
+omitted,
+the
+scheme
+is
+assumed
+to
+be
+<code>
+coap
+</code>.
+</dd>
+</dl>
+</div>
+<p>
+<a href="#sequence-dnssd-thing" class="fig-ref" title= "Using mDNS for discovery of the Thing Description of a Thing">
+Figure
+<bdi class="">
+2
+</bdi>
+</a>
+and
+<a href="#sequence-dnssd-directory" class="fig-ref" title= "Using mDNS for discovery of the Thing Description of a Thing Description Directory (TDD)">
+Figure
+<bdi class="">
+3
+</bdi>
+</a>
+shows
+example
+sequences
+supporting
+discovery
+of
+a
+Thing
+or
+a
+<a href= "#dfn-wot-thing-description-directory" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-wot-thing-description-directory-10">
+Thing
+Description
+Directory
+</a>
+using
+DNS-SD
+and
+mDNS.
+</p>
+<figure id="sequence-dnssd-thing">
+<img src= "images/sequence-dnssd-thing.png" srcset= "images/sequence-dnssd-thing.svg" class="wot-diagram" alt= "An example sequence of discovery of Thing using DNS-SD and mDNS" />
+<figcaption>
+<a class="self-link" href= "#sequence-dnssd-thing">
+Figure
+<bdi class="figno">
+2
+</bdi>
+</a>
+<span class="fig-title">
+Using
+mDNS
+for
+discovery
+of
+the
+Thing
+Description
+of
+a
+Thing
+</span>
+</figcaption>
+</figure>
+<figure id="sequence-dnssd-directory">
+<img src= "images/sequence-dnssd-directory.png" srcset= "images/sequence-dnssd-directory.svg" class="wot-diagram" alt= "An example sequence of discovery of directory service using DNS-SD and mDNS" />
+<figcaption>
+<a class="self-link" href= "#sequence-dnssd-directory">
+Figure
+<bdi class="figno">
+3
+</bdi>
+</a>
+<span class="fig-title">
+Using
+mDNS
+for
+discovery
+of
+the
+Thing
+Description
+of
+a
+Thing
+Description
+Directory
+(TDD)
+</span>
+</figcaption>
+</figure>
+</section>
+<section id="introduction-core-rd-sec" class="normative">
+<div class="header-wrapper">
+<h3 id="x6-4-core-link-format-and-core-resource-directory">
+<bdi class="secno">
+6.4
+</bdi>
+CoRE
+Link
+Format
+and
+CoRE
+Resource
+Directory
+</h3>
+<a class="self-link" href="#introduction-core-rd-sec" aria-label= "Permalink for Section 6.4">
+</a>
+</div>
+<p>
+<span class="rfc2119-assertion" id="introduction-core-rd">
+A
+Thing
+or
+<a href="#dfn-wot-thing-description-directory" class= "internalDFN" data-link-type="dfn" id= "ref-for-dfn-wot-thing-description-directory-11">
+Thing
+Description
+Directory
+</a>
+<em class="rfc2119">
+MAY
+</em>
+advertise
+its
+presence
+using
+the
+Constrained
+RESTful
+Environment
+(CoRE)
+Link
+Format
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href= "#bib-rfc6690" title= "Constrained RESTful Environments (CoRE) Link Format">
+RFC6690
+</a>
+</cite>
+].
+</span>
+<span class="rfc2119-assertion" id= "introduction-core-rd-directory">
+A
+<a href="#dfn-thing" class= "internalDFN" data-link-type="dfn" id= "ref-for-dfn-thing-1">
+Thing
+</a>
+or
+<a href= "#dfn-wot-thing-description-directory" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-wot-thing-description-directory-12">
+Thing
+Description
+Directory
+</a>
+<em class="rfc2119">
+MAY
+</em>
+use
+the
+CoRE
+Resource
+Directory
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href= "#bib-rfc9176" title= "Constrained RESTful Environments (CoRE) Resource Directory">
+RFC9176
+</a>
+</cite>
+]
+to
+register
+a
+link
+to
+its
+corresponding
+Thing
+Description.
+</span>
+</p>
+<p>
+<span class="rfc2119-assertion" id= "introduction-core-rd-resource-type-thing">
+The
+resource
+type
+(
+<code>
+rt
+</code>
+)
+of
+the
+Link
+that
+targets
+the
+Thing
+Description
+of
+the
+Thing
+<em class="rfc2119">
+MUST
+</em>
+be
+<code>
+wot.thing
+</code>.
+</span>
+<span class="rfc2119-assertion" id= "introduction-core-rd-resource-type-directory">
+The
+resource
+type
+of
+the
+Link
+that
+targets
+the
+Thing
+Description
+of
+the
+<a href= "#dfn-wot-thing-description-directory" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-wot-thing-description-directory-13">
+Thing
+Description
+Directory
+</a>
+<em class="rfc2119">
+MUST
+</em>
+be
+<code>
+wot.directory
+</code>.
+</span>
+</p>
+</section>
+<section id="introduction-did-sec" class="normative">
+<div class="header-wrapper">
+<h3 id="x6-5-did-documents">
+<bdi class="secno">
+6.5
+</bdi>
+DID
+Documents
+</h3>
+<a class="self-link" href="#introduction-did-sec" aria-label= "Permalink for Section 6.5">
+</a>
+</div>
+<p>
+<span class="rfc2119-assertion" id="introduction-did">
+A
+<a href= "#dfn-thing" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-thing-2">
+Thing
+</a>
+or
+<a href= "#dfn-wot-thing-description-directory" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-wot-thing-description-directory-14">
+Thing
+Description
+Directory
+</a>
+using
+a
+Decentralized
+Identifier
+(DID)
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href= "#bib-did-core" title= "Decentralized Identifiers (DIDs) v1.0">
+DID-CORE
+</a>
+</cite>
+]
+<em class="rfc2119">
+MAY
+</em>
+advertise
+the
+location
+of
+its
+<a href= "#dfn-td" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-td-1">
+TD
+</a>
+by
+including
+a
+DID
+Service
+Endpoint
+of
+type
+<code>
+WotThing
+</code>
+or
+<code>
+WotDirectory
+</code>,
+respectively,
+in
+the
+DID
+Document
+that
+the
+TD's
+identifier
+resolves
+to.
+</span>
+</p>
+<p>
+<span class="rfc2119-assertion" id= "introduction-did-service-context">
+In
+order
+to
+define
+Service
+Endpoints
+for
+WoT
+Discovery,
+the
+DID
+Document
+obtained
+by
+resolving
+the
+DID
+of
+a
+<a href="#dfn-thing" class="internalDFN" data-link-type="dfn" id="ref-for-dfn-thing-3">
+Thing
+</a>
+or
+<a href= "#dfn-wot-thing-description-directory" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-wot-thing-description-directory-15">
+Thing
+Description
+Directory
+</a>
+<em class="rfc2119">
+MUST
+</em>
+include
+the
+URL
+<code>
+https://www.w3.org/2022/wot/discovery-did
+</code>
+in
+its
+<code>
+@context
+</code>
+[
+<cite>
+<a class="bibref" data-link-type= "biblio" href="#bib-did-spec-registries" title= "DID Specification Registries">
+did-spec-registries
+</a>
+</cite>
+].
+</span>
+</p>
+<p>
+<span class="rfc2119-assertion" id= "introduction-did-service-endpoint">
+If
+the
+DID
+Document
+obtained
+by
+resolving
+the
+DID
+of
+a
+<a href="#dfn-thing" class="internalDFN" data-link-type="dfn" id="ref-for-dfn-thing-4">
+Thing
+</a>
+or
+<a href= "#dfn-wot-thing-description-directory" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-wot-thing-description-directory-16">
+Thing
+Description
+Directory
+</a>
+contains
+a
+Service
+Endpoint
+of
+type
+<code>
+WotThing
+</code>
+or
+<code>
+WotDirectory
+</code>,
+respectively,
+then
+this
+Service
+Endpoint
+<em class="rfc2119">
+MUST
+</em>
+refer
+to
+the
+<a href="#dfn-td" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-td-2">
+TD
+</a>
+describing
+that
+Thing
+(when
+using
+the
+<code>
+WotThing
+</code>
+service
+name)
+or
+the
+<a href="#dfn-td" class= "internalDFN" data-link-type="dfn" id="ref-for-dfn-td-3">
+TD
+</a>
+describing
+that
+<a href="#dfn-wot-thing-description-directory" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-wot-thing-description-directory-17">
+Thing
+Description
+Directory
+</a>
+(when
+using
+the
+<code>
+WotDirectory
+</code>
+service
+name),
+respectively
+[
+<cite>
+<a class="bibref" data-link-type= "biblio" href="#bib-did-spec-registries" title= "DID Specification Registries">
+did-spec-registries
+</a>
+</cite>
+].
+</span>
+</p>
+<aside class="example" id= "example-a-example-service-endpoint-in-a-did-document-wotthing">
+<div class="marker">
+<a class="self-link" href= "#example-a-example-service-endpoint-in-a-did-document-wotthing">
+Example
+<bdi>
+1
+</bdi>
+</a>
+<span class="example-title">:
+A
+Example
+Service
+Endpoint
+in
+a
+DID
+Document
+-
+WotThing
+</span>
+</div>
+<pre aria-busy="false"><code class="hljs javascript">{
+    <span class="hljs-string">"@context"</span>:[
+        <span class=
+"hljs-string">"https://www.w3.org/ns/did/v1"</span>,
+        <span class=
+"hljs-string">"https://www.w3.org/2022/wot/discovery-did"</span>
+    ],
+    ...
+    <span class="hljs-string">"service"</span>: [{
+        <span class="hljs-string">"id"</span>: <span class=
+"hljs-string">"did:example:wotdiscoveryexample#td"</span>,
+        <span class="hljs-string">"type"</span>: <span class=
+"hljs-string">"WotThing"</span>,
+        <span class="hljs-string">"serviceEndpoint"</span>:
+            <span class=
+"hljs-string">"https://wot.example.com/.well-known/wot"</span>
+    }]
+    ...
+}
+</code>
+</pre>
+</aside>
+<aside class="example" id= "example-a-example-service-endpoint-in-a-did-document-wotdirectory">
+<div class="marker">
+<a class="self-link" href= "#example-a-example-service-endpoint-in-a-did-document-wotdirectory">
+Example
+<bdi>
+2
+</bdi>
+</a>
+<span class="example-title">:
+A
+Example
+Service
+Endpoint
+in
+a
+DID
+Document
+-
+WotDirectory
+</span>
+</div>
+<pre aria-busy="false"><code class="hljs javascript">{
+    <span class="hljs-string">"@context"</span>:[
+        <span class=
+"hljs-string">"https://www.w3.org/ns/did/v1"</span>,
+        <span class=
+"hljs-string">"https://www.w3.org/2022/wot/discovery-did"</span>
+    ],
+    ...
+    <span class="hljs-string">"service"</span>: [{
+        <span class="hljs-string">"id"</span>: <span class=
+"hljs-string">"did:example:wotdiscoveryexample#tdd"</span>,
+        <span class="hljs-string">"type"</span>: <span class=
+"hljs-string">"WotDirectory"</span>,
+        <span class="hljs-string">"serviceEndpoint"</span>:
+            <span class=
+"hljs-string">"https://wot.example.com/tdd"</span>
+    }]
+    ...
+}
+</code>
+</pre>
+</aside>
+</section>
+</section>
+<section id="exploration-mech" class="normative">
+<div class="header-wrapper">
+<h2 id="x7-exploration-mechanisms">
+<bdi class="secno">
+7.
+</bdi>
+Exploration
+Mechanisms
+</h2>
+<a class="self-link" href="#exploration-mech" aria-label= "Permalink for Section 7.">
+</a>
+</div>
+This
+section
+defines
+the
+supported
+exploration
+mechanisms
+after
+providing
+some
+common
+background
+material.
+<section id="exploration-overview" class="normative">
+<div class="header-wrapper">
+<h3 id="x7-1-overview">
+<bdi class="secno">
+7.1
+</bdi>
+Overview
+</h3>
+<a class="self-link" href="#exploration-overview" aria-label= "Permalink for Section 7.1">
+</a>
+</div>
+<figure id="exploration-class-diagram">
+<img src= "images/exploration-class-diagram.svg" class="wot-diagram" alt= "Exploration mechanisms high-level class diagram" />
+<figcaption>
+<a class="self-link" href= "#exploration-class-diagram">
+Figure
+<bdi class="figno">
+4
+</bdi>
+</a>
+<span class="fig-title">
+The
+high-level
+class
+diagram
+of
+the
+exploration
+mechanisms,
+depicting
+how
+Thing
+Description
+Servers
+and
+Thing
+Description
+Directories
+provide
+<a href="#dfn-td" class= "internalDFN" data-link-type="dfn" id="ref-for-dfn-td-4">
+TDs
+</a>.
+A
+Self-describing
+Thing
+is
+a
+special
+case
+of
+a
+Thing
+Description
+Server
+that
+is
+also
+a
+Thing.
+A
+Thing
+Description
+Directory
+acts
+as
+a
+Thing
+Description
+Server
+for
+each
+Thing
+Description
+it
+contains.
+</span>
+</figcaption>
+</figure>
+<p>
+<a href="#exploration-class-diagram" data-matched-text= "[[[#exploration-class-diagram]]]" class="fig-ref" title= "The high-level class diagram of the exploration mechanisms, depicting how Thing Description Servers and Thing Description Directories provide TDs. A Self-describing Thing is a special case of a Thing Description Server that is also a Thing. A Thing Description Directory acts as a Thing Description Server for each Thing Description it contains.">
+Figure
+<bdi class="">
+4
+</bdi>
+</a>
+depicts
+the
+high-level
+information
+model
+for
+<a href="#dfn-wot-td-server" class="internalDFN" data-link-type="dfn" id="ref-for-dfn-wot-td-server-1">
+TD
+Servers
+</a>
+(serving
+single
+TDs,
+including
+those
+for
+self-description)
+and
+<a href= "#dfn-wot-thing-description-directory" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-wot-thing-description-directory-18">
+Thing
+Description
+Directory
+</a>
+services.
+A
+<a href= "#dfn-wot-thing-description-directory" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-wot-thing-description-directory-19">
+Thing
+Description
+Directory
+</a>
+may
+contain
+<a href="#dfn-td" class="internalDFN" data-link-type="dfn" id="ref-for-dfn-td-5">
+TDs
+</a>
+and
+at
+the
+same
+time
+is
+also
+a
+Thing,
+which
+means
+it
+has
+its
+own
+TD.
+A
+directory
+also
+hosts
+web
+service
+endpoints
+for
+retrieving
+individual
+TDs
+for
+other
+Things
+and
+each
+of
+these
+can
+be
+used
+as
+a
+TD
+Server.
+A
+Thing
+may
+in
+general
+host
+its
+own
+TD
+in
+which
+case
+it
+is
+a
+Self-Describing
+Thing.
+Self-description
+is
+not
+mandatory
+for
+directories,
+but
+Self-Describing
+Thing
+Description
+Directories
+are
+possible
+that
+are
+both
+Thing
+Description
+Directories
+and
+Self-Describing
+Things.
+</p>
+<p>
+The
+two
+basic
+exploration
+mechanisms
+are
+described
+in
+<a href= "#exploration-server" data-matched-text="[[[#exploration-server]]]" class="sec-ref">
+<bdi class="secno">
+7.2
+</bdi>
+Thing
+Description
+Server
+</a>
+and
+<a href="#exploration-directory" data-matched-text= "[[[#exploration-directory]]]" class="sec-ref">
+<bdi class= "secno">
+7.3
+</bdi>
+Thing
+Description
+Directory
+</a>.
+</p>
+<section id="exploration-ontology" class="normative">
+<div class="header-wrapper">
+<h4 id="x7-1-1-ontology">
+<bdi class="secno">
+7.1.1
+</bdi>
+Ontology
+</h4>
+<a class="self-link" href="#exploration-ontology" aria-label= "Permalink for Section 7.1.1">
+</a>
+</div>
+<figure id="discovery-class-diagram-ontology">
+<img src= "images/discovery-class-diagram-ontology.svg" class="wot-diagram" alt="Ontology of TD in discovery context" />
+<figcaption>
+<a class="self-link" href= "#discovery-class-diagram-ontology">
+Figure
+<bdi class= "figno">
+5
+</bdi>
+</a>
+<span class="fig-title">
+The
+ontology
+of
+Thing
+Descriptions
+in
+the
+Discovery
+context.
+</span>
+</figcaption>
+</figure>
+<p>
+<a href="#discovery-class-diagram-ontology" data-matched-text= "[[[#discovery-class-diagram-ontology]]]" class="fig-ref" title= "The ontology of Thing Descriptions in the Discovery context.">
+Figure
+<bdi class="">
+5
+</bdi>
+</a>
+illustrates
+the
+Discovery
+ontology
+as
+an
+extension
+of
+the
+Thing
+ontology.
+</p>
+<p>
+The
+ontology
+includes
+a
+class
+for
+metadata
+that
+are
+associated
+with
+TDs
+stored
+in
+a
+directory.
+This
+class
+is
+called
+<code>
+RegistrationInformation
+</code>
+and
+described
+as
+part
+of
+the
+directory
+specification
+in
+<a href= "#exploration-directory-registration-info" data-matched-text= "[[[#exploration-directory-registration-info]]]" class= "sec-ref">
+<bdi class="secno">
+7.3.1.1
+</bdi>
+Registration
+Information
+</a>.
+</p>
+<p>
+The
+Discovery
+ontology
+also
+defines
+two
+new
+Thing
+Description
+classes,
+described
+in
+the
+following
+sections,
+that
+may
+be
+used
+to
+model
+special
+exploratory
+metadata:
+<a href= "#exploration-td-type-thingdirectory">
+ThingDirectory
+</a>
+and
+<a href="#exploration-td-type-thinglink">
+ThingLink
+</a>.
+</p>
+<section id="exploration-td-type-thingdirectory" class="normative">
+<div class="header-wrapper">
+<h5 id="x7-1-1-1-thingdirectory">
+<bdi class="secno">
+7.1.1.1
+</bdi>
+<code>
+ThingDirectory
+</code>
+</h5>
+<a class="self-link" href="#exploration-td-type-thingdirectory" aria-label="Permalink for Section 7.1.1.1">
+</a>
+</div>
+<span class="rfc2119-assertion" id= "exploration-directory-description-type">
+A
+TD
+which
+describes
+a
+Thing
+Description
+Directory
+instance
+<em class="rfc2119">
+MUST
+</em>
+use
+type
+<code>
+ThingDirectory
+</code>
+from
+the
+discovery
+context
+or
+URI
+<code>
+https://www.w3.org/2022/wot/discovery#ThingDirectory
+</code>.
+</span>
+<p>
+A
+TD
+of
+this
+class
+can
+be
+derived
+from
+Directory's
+Thing
+Model;
+see
+<a href="#directory-api-spec" data-matched-text= "[[[#directory-api-spec]]]" class="sec-ref">
+<bdi class= "secno">
+7.3.2.4
+</bdi>
+API
+Specification
+(Thing
+Model)
+</a>.
+</p>
+</section>
+<section id="exploration-td-type-thinglink" class="normative">
+<div class="header-wrapper">
+<h5 id="x7-1-1-2-thinglink">
+<bdi class="secno">
+7.1.1.2
+</bdi>
+<code>
+ThingLink
+</code>
+</h5>
+<a class="self-link" href="#exploration-td-type-thinglink" aria-label="Permalink for Section 7.1.1.2">
+</a>
+</div>
+<span class="rfc2119-assertion" id= "exploration-link-description-type">
+A
+TD
+which
+describes
+a
+reference
+to
+another
+TD
+<em class="rfc2119">
+MUST
+</em>
+use
+type
+<code>
+ThingLink
+</code>
+from
+the
+discovery
+context
+or
+URI
+<code>
+https://www.w3.org/2022/wot/discovery#ThingLink
+</code>.
+</span>
+<span class="rfc2119-assertion" id= "exploration-link-description-link">
+A
+Thing
+Link
+<em class= "rfc2119">
+MUST
+</em>
+define
+the
+referenced
+TD
+as
+a
+Link
+with
+<code>
+describedby
+</code>
+link
+relation
+type,
+<code>
+application/td+json
+</code>
+media
+type
+and
+<code>
+href
+</code>
+set
+to
+the
+target
+URL.
+</span>
+<p>
+<a href="#example-td-link-type" data-matched-text= "[[[#example-td-link-type]]]" class="box-ref">
+Example
+<bdi>
+3
+</bdi>
+</a>
+is
+an
+example
+Thing
+Link.
+</p>
+<aside class="example" id="example-td-link-type">
+<div class="marker">
+<a class="self-link" href= "#example-td-link-type">
+Example
+<bdi>
+3
+</bdi>
+</a>
+<span class= "example-title">:
+Example
+of
+a
+Thing
+Link,
+referencing
+a
+remote
+TD
+</span>
+</div>
+<pre aria-busy="false"><code class="hljs json">{
+    <span class="hljs-attr">"@context"</span>: [
+        <span class=
+"hljs-string">"https://www.w3.org/2022/wot/td/v1.1"</span>,
+        <span class=
+"hljs-string">"https://www.w3.org/2022/wot/discovery"</span>
+    ],
+    <span class="hljs-attr">"@type"</span>: <span class=
+"hljs-string">"ThingLink"</span>,
+    <span class="hljs-attr">"id"</span>: <span class=
+"hljs-string">"urn:example:link"</span>,
+    <span class="hljs-attr">"links"</span>: [{
+        <span class="hljs-attr">"rel"</span>: <span class=
+"hljs-string">"describedby"</span>,
+        <span class="hljs-attr">"href"</span>: <span class=
+"hljs-string">"https://example.com/td.jsonld"</span>,
+        <span class="hljs-attr">"type"</span>: <span class=
+"hljs-string">"application/td+json"</span>
+    }],
+    <span class="hljs-attr">"security"</span>: <span class=
+"hljs-string">"nosec_sc"</span>,
+    <span class="hljs-attr">"securityDefinitions"</span>: {
+        <span class="hljs-attr">"nosec_sc"</span>: {
+            <span class="hljs-attr">"scheme"</span>: <span class=
+"hljs-string">"nosec"</span>
+        }
+    },
+    <span class="hljs-attr">"title"</span>: <span class=
+"hljs-string">"Example TD referencing another"</span>
+}
+</code>
+</pre>
+</aside>
+<p>
+A
+Thing
+Link
+can
+be
+used
+in
+various
+scenarios.
+For
+example:
+</p>
+<ul>
+<li>
+A
+self-describing
+Thing
+with
+limited
+computational
+resources
+intends
+to
+describe
+itself:
+host
+a
+minimal
+<a href="#dfn-td" class= "internalDFN" data-link-type="dfn" id="ref-for-dfn-td-6">
+TD
+</a>
+(Thing
+Link)
+locally
+and
+references
+a
+larger
+one
+with
+the
+full
+details
+hosted
+at
+a
+different
+URL,
+perhaps
+in
+a
+directory.
+</li>
+<li>
+A
+self-describing
+Thing
+or
+proxy
+has
+a
+very
+large
+or
+dynamic
+description:
+registers
+a
+small
+or
+static
+<a href="#dfn-td" class= "internalDFN" data-link-type="dfn" id="ref-for-dfn-td-7">
+TD
+</a>
+(Thing
+Link)
+in
+a
+directory
+which
+references
+the
+actual
+<a href= "#dfn-td" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-td-8">
+TD
+</a>
+hosted
+at
+the
+edge.
+</li>
+</ul>
+</section>
+</section>
+<section id="exploration-secboot" class="normative">
+<div class="header-wrapper">
+<h4 id="x7-1-2-security-bootstrapping">
+<bdi class= "secno">
+7.1.2
+</bdi>
+Security
+Bootstrapping
+</h4>
+<a class="self-link" href="#exploration-secboot" aria-label= "Permalink for Section 7.1.2">
+</a>
+</div>
+<p>
+The
+purpose
+of
+an
+exploration
+service
+is
+to
+serve
+TDs,
+but
+only
+after
+suitable
+authentication,
+and
+only
+to
+authorized
+parties.
+However,
+in
+some
+cases
+a
+Discoverer
+may
+not
+know
+what
+security
+credentials
+are
+needed
+to
+access
+a
+TD
+via
+an
+exploration
+service,
+particularly
+in
+ad-hoc
+scenarios.
+Since
+upon
+first
+access
+to
+an
+exploration
+service
+a
+Discoverer
+will
+not
+yet
+have
+access
+to
+the
+TD
+if
+suitable
+authentication
+credentials
+are
+not
+provided,
+the
+Discoverer
+can't
+depend
+on
+the
+security
+metadata
+held
+in
+TDs
+to
+know
+what
+kind
+of
+authentication
+and
+authorization
+information
+is
+needed.
+If
+the
+Discoverer
+has
+no
+prior
+knowledge,
+it
+will
+have
+to
+depend
+on
+existing
+security
+negotation
+support
+to
+bootstrap
+access,
+at
+least
+to
+the
+TD
+itself.
+</p>
+<p>
+We
+define
+the
+following
+for
+the
+HTTP
+protocol,
+for
+which
+security
+negotiation
+processes
+already
+exist.
+However,
+most
+of
+the
+HTTP
+negotiation
+processes
+assume
+there
+is
+a
+human
+user
+in
+the
+loop,
+but
+this
+is
+also
+appropriate
+for
+WoT
+Discovery,
+since
+this
+problem
+will
+typically
+occur
+when
+a
+user
+is
+trying
+to
+access
+a
+public
+WoT
+service
+or
+perform
+integration
+of
+a
+new
+device.
+In
+this
+case
+the
+purpose
+of
+negotiation
+is
+to
+provide
+guidance
+on
+what
+credentials
+are
+needed
+to
+access
+the
+system.
+</p>
+<p>
+In
+cases
+when
+exploration
+services
+are
+being
+used
+to
+automate
+system
+management
+it
+would
+be
+best
+to
+pre-establish
+what
+credentials
+(and
+authentication
+mechanisms)
+are
+needed
+to
+access
+the
+relevant
+exploration
+services
+and
+security
+bootstrapping
+would
+not
+be
+required.
+For
+this
+reason
+security
+bootstrapping
+is
+not
+a
+mandatory
+feature,
+and
+can
+be
+omitted
+or
+disabled
+on
+devices
+that
+are
+to
+be
+used
+with
+pre-established
+security
+mechanisms.
+</p>
+<p>
+Security
+bootstrapping
+may
+also
+only
+be
+necessary
+on
+the
+<em>
+first
+</em>
+access
+to
+a
+TD.
+Once
+a
+Discoverer
+has
+determined
+what
+credentials
+and
+authentication
+mechanism
+are
+required
+to
+access
+a
+particular
+exploration
+service,
+they
+can
+retain
+this
+information
+and
+attempt
+to
+use
+them
+for
+future
+accesses.
+Note
+however
+that
+depending
+on
+the
+security
+scheme
+used,
+credentials
+themselves
+may
+expire
+and
+may
+need
+to
+be
+re-established
+periodically.
+</p>
+<p>
+<span class="rfc2119-assertion" id= "security-bootstrapping-endpoints">
+Security
+bootstrapping
+<em class="rfc2119">
+MAY
+</em>
+be
+provided
+on
+any
+HTTP
+endpoint
+that
+serves
+a
+TD.
+</span>
+As
+mentioned
+above,
+disabling
+or
+omitting
+security
+bootstrapping
+is
+permissible
+if
+security
+mechanisms
+have
+been
+previously
+established.
+For
+example,
+if
+an
+installation
+wants
+to
+use
+the
+OAuth2
+<code>
+client
+</code>
+flow
+and
+provide
+potential
+clients
+with
+an
+address
+of
+an
+authentication
+server
+to
+use
+in
+advance,
+then
+security
+bootstrapping
+can
+be
+disabled,
+since
+the
+alternative
+would
+be
+to
+include
+other
+(and
+potentially
+weaker)
+forms
+of
+authentication.
+</p>
+<p>
+In
+the
+HTTP
+protocol,
+the
+authentication
+and
+authorization
+mechanisms
+to
+be
+used
+can
+generally
+be
+negotiated
+by
+the
+HTTP
+server
+returning
+a
+"401
+(Unauthorized)"
+response
+code
+in
+conjunction
+with
+a
+<code>
+WWW-Authenticate
+</code>
+header
+that
+specifies
+the
+information
+required.
+To
+gain
+access,
+the
+client
+then
+needs
+to
+make
+another
+request
+with
+the
+necessary
+information.
+<a href= "https://www.iana.org/assignments/http-authschemes/http-authschemes.xhtml">
+There
+are
+several
+authentication
+schemes
+registered
+with
+IANA.
+</a>
+However,
+not
+all
+of
+these
+are
+in
+wide
+use,
+some
+are
+experimental,
+and
+there
+is
+only
+partial
+overlap
+with
+the
+schemes
+supported
+by
+TDs.
+Also,
+note
+that
+the
+<code>
+oauth
+</code>
+scheme
+in
+the
+IANA
+registration
+refers
+to
+OAuth1,
+which
+is
+deprecated,
+so
+it
+should
+not
+be
+used.
+The
+relevant
+OAuth2
+flow,
+the
+<code>
+code
+</code>
+flow,
+instead
+of
+a
+401
+response
+begins
+with
+a
+redirection
+to
+an
+authentication
+server,
+eventually
+resulting
+in
+credentials
+(bearer
+tokens
+in
+the
+case
+of
+WoT)
+that
+can
+be
+used
+for
+access.
+</p>
+<p>
+Given
+these
+considerations,
+to
+enable
+security
+bootstrapping
+on
+a
+wide
+variety
+of
+devices
+as
+well
+as
+on
+browsers,
+the
+following
+constraints
+should
+be
+observed:
+</p>
+<ul>
+<li>
+<span class="rfc2119-assertion" id="exploration-secboot-401">
+If
+security
+bootstrapping
+is
+enabled
+on
+an
+exploration
+service,
+after
+initial
+contact
+using
+the
+URL
+provided
+by
+an
+introduction
+mechanism,
+the
+exploration
+service
+<em class="rfc2119">
+MUST
+</em>
+reply
+with
+an
+HTTP
+response
+code
+appropriate
+for
+one
+of
+the
+Basic,
+Bearer,
+Digest,
+or
+OAuth2
+security
+schemes
+if
+authentication
+information
+has
+not
+been
+provided
+but
+access
+can
+be
+granted
+when
+it
+is.
+</span>
+Note
+that
+if
+the
+exploration
+service
+does
+not
+want
+to
+provide
+access
+for
+some
+reason,
+or
+if
+security
+bootstrapping
+is
+disabled,
+it
+can
+ignore
+the
+request
+or
+reply
+with
+another
+code
+such
+as
+404
+or
+403.
+Also,
+if
+no
+authentication
+is
+required,
+then
+the
+system
+can
+reply
+immediately
+with
+the
+requested
+TD
+as
+if
+authentication
+information
+were
+provided.
+Bypassing
+authentication
+however
+is
+only
+appropriate
+if
+the
+TD
+served
+as
+a
+response
+does
+not
+contain
+and
+cannot
+be
+used
+to
+infer
+Personally
+Identifiable
+Information;
+see
+<a href="#privacy-considerations" class= "sec-ref">
+<bdi class="secno">
+9.
+</bdi>
+Privacy
+Considerations
+</a>.
+</li>
+<li>
+If
+security
+bootstrapping
+is
+enabled
+on
+an
+exploration
+service
+using
+one
+of
+the
+following
+IANA-registered
+HTTP
+Authentication
+Schemes:
+Basic,
+Bearer,
+or
+Digest,
+then
+(following
+the
+standards
+for
+these
+authentication
+schemes)
+a
+401
+HTTP
+response
+at
+an
+API
+endpoint
+intended
+to
+serve
+a
+TD
+must
+include
+a
+<code>
+WWW-Authenticate
+</code>
+header
+and
+any
+other
+headers
+describing
+the
+required
+authorizations.
+For
+details
+of
+the
+requirements,
+the
+IANA
+registry
+should
+be
+consulted
+for
+each
+of
+the
+above
+authentication
+schemes.
+Likewise,
+following
+the
+OAuth2
+specifications,
+if
+the
+OAuth2
+<code>
+code
+</code>
+flow
+is
+used
+during
+security
+bootstrapping,
+the
+"302
+(Found)"
+or
+"303
+(See
+Other)"
+response
+code
+must
+be
+used
+for
+redirection
+to
+the
+authentication
+server,
+with
+access
+credentials
+eventually
+being
+represented
+with
+bearer
+tokens.
+Note
+that
+the
+other
+OAuth2
+flow
+supported
+in
+WoT
+Thing
+Description
+1.1,
+<code>
+client
+</code>,
+expects
+the
+initial
+access
+to
+be
+to
+the
+authentication
+server,
+not
+the
+final
+endpoint,
+and
+so
+cannot
+be
+used
+via
+security
+bootstrapping.
+These
+requirements
+also
+apply
+only
+to
+endpoints
+of
+exploration
+services
+that
+might
+need
+to
+support
+security
+bootstrapping,
+that
+is
+those
+that
+serve
+TDs,
+not
+to
+other
+endpoints
+that
+might
+be
+provided
+by
+the
+same
+exploration
+service.
+In
+particular,
+these
+requirements
+apply
+only
+to
+URLs
+that
+can
+be
+referenced
+by
+introduction
+mechanisms,
+not
+to
+(for
+example)
+event
+subscription
+endpoints.
+</li>
+</ul>
+<p>
+There
+are
+relevant
+Security
+and
+Privacy
+Considerations
+in
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href= "#bib-wot-architecture11" title= "Web of Things (WoT) Architecture 1.1">
+wot-architecture11
+</a>
+</cite>
+]
+and
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href= "#bib-wot-thing-description11" title= "Web of Things (WoT) Thing Description 1.1">
+wot-thing-description11
+</a>
+</cite>
+]
+regarding
+when
+authentication
+is
+required
+for
+access
+to
+TDs
+and
+the
+use
+of
+secure
+transport.
+See
+also
+<a href="#privacy-considerations" data-matched-text="[[[#privacy-considerations]]]" class= "sec-ref">
+<bdi class="secno">
+9.
+</bdi>
+Privacy
+Considerations
+</a>.
+In
+summary,
+secure
+transport
+(e.g.
+TLS)
+is
+required
+for
+public
+services
+and
+strongly
+recommended
+even
+on
+private
+networks
+(even
+if
+there
+is
+no
+authentication
+requirement,
+to
+protect
+the
+confidentiality
+of
+queries),
+and
+serving
+requests
+without
+authentication
+and
+authorization
+should
+only
+be
+considered
+in
+limited
+circumstances
+when
+no
+Personally
+Identifiable
+Information
+is
+present
+or
+can
+be
+inferred.
+</p>
+</section>
+</section>
+<section id="exploration-server" class="normative">
+<div class="header-wrapper">
+<h3 id="x7-2-thing-description-server">
+<bdi class="secno">
+7.2
+</bdi>
+Thing
+Description
+Server
+</h3>
+<a class="self-link" href="#exploration-server" aria-label= "Permalink for Section 7.2">
+</a>
+</div>
+<p>
+Any
+web
+service
+that
+can
+be
+referenced
+by
+a
+URL
+and
+return
+a
+TD
+with
+appropriate
+authentication
+and
+access
+controls
+can
+be
+used
+as
+an
+exploration
+mechanism.
+We
+will
+refer
+to
+this
+as
+a
+Thing
+Description
+Server
+or
+TD
+Server.
+A
+TD
+Server
+does
+not
+need
+to
+be
+a
+Thing.
+In
+particular,
+a
+TD
+can
+be
+hosted
+on
+an
+ordinary
+web
+server
+and
+referenced
+by
+its
+URL.
+</p>
+<p>
+A
+TD
+Server
+can
+be
+used
+to
+support
+self-description.
+For
+self-description,
+a
+<a href="#dfn-thing" class="internalDFN" data-link-type="dfn" id="ref-for-dfn-thing-5">
+Thing
+</a>
+hosts
+its
+own
+<a href="#dfn-td" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-td-9">
+TD
+</a>
+and
+makes
+it
+available
+via
+a
+web
+resource
+identified
+with
+a
+URL.
+Such
+a
+web
+resource
+however
+is
+not
+included
+as
+an
+affordance
+in
+the
+TD
+itself.
+This
+web
+resource
+may
+or
+may
+not
+be
+the
+same
+as
+the
+well-known
+URL
+used
+as
+an
+Introduction
+mechanism
+defined
+in
+<a href="#introduction-well-known" class= "sec-ref">
+<bdi class="secno">
+6.2
+</bdi>
+Well-Known
+URIs
+</a>.
+</p>
+<p>
+Use
+of
+secure
+transport
+is
+subject
+to
+assertions
+given
+in
+the
+Security
+Considerations
+and
+Privacy
+Considerations
+sections
+of
+the
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href= "#bib-wot-architecture11" title= "Web of Things (WoT) Architecture 1.1">
+wot-architecture11
+</a>
+</cite>
+]
+and
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href= "#bib-wot-thing-description11" title= "Web of Things (WoT) Thing Description 1.1">
+wot-thing-description11
+</a>
+</cite>
+]
+specifications,
+which
+define
+scenarios
+where
+secure
+transport
+is
+recommended
+or
+mandatory
+and
+mutual
+authentication
+is
+recommended.
+</p>
+<p>
+A
+TD
+Server
+distributing
+a
+TD
+using
+the
+following
+protocols
+is
+subject
+to
+the
+following
+constraints:
+</p>
+<dl>
+<dt>
+HTTP
+</dt>
+<dd>
+<p>
+<span class="rfc2119-assertion" id= "exploration-server-http-method">
+An
+HTTP-based
+TD
+Server
+providing
+a
+<a href="#dfn-td" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-td-10">
+TD
+</a>
+<em class="rfc2119">
+MUST
+</em>
+serve
+that
+resource
+with
+a
+<code>
+GET
+</code>
+method.
+</span>
+<span class= "rfc2119-assertion" id="exploration-server-http-resp">
+A
+successful
+response
+from
+an
+HTTP-based
+TD
+Server
+providing
+a
+<a href="#dfn-td" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-td-11">
+TD
+</a>
+<em class="rfc2119">
+MUST
+</em>
+have
+200
+(OK)
+status
+and
+the
+<a href="#dfn-td" class="internalDFN" data-link-type="dfn" id="ref-for-dfn-td-12">
+TD
+</a>
+in
+the
+body.
+</span>
+<span class="rfc2119-assertion" id= "exploration-server-http-resp-content-type">
+A
+successful
+response
+with
+JSON
+serialization
+<em class="rfc2119">
+MUST
+</em>
+contain
+either
+<code>
+application/json
+</code>
+or
+<code>
+application/td+json
+</code>
+in
+the
+Content-Type
+header.
+</span>
+Here
+<code>
+application/td+json
+</code>
+is
+preferred
+as
+it
+is
+more
+specific
+and
+implies
+<code>
+application/json
+</code>.
+<span class= "rfc2119-assertion" id="exploration-server-http-resp-json">
+The
+default
+serialization
+format
+for
+successful
+response
+bodies
+<em class="rfc2119">
+MUST
+</em>
+be
+JSON,
+with
+JSON-LD
+1.1
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href= "#bib-json-ld11" title="JSON-LD 1.1">
+JSON-LD11
+</a>
+</cite>
+]
+syntax.
+</span>
+The
+JSON-LD
+syntax
+allows
+semantic
+extensions
+and
+processing.
+<span class="rfc2119-assertion" id= "exploration-server-http-alternate-content">
+An
+HTTP-based
+TD
+Server
+providing
+a
+<a href="#dfn-td" class="internalDFN" data-link-type= "dfn" id="ref-for-dfn-td-13">
+TD
+</a>
+<em class="rfc2119">
+MAY
+</em>
+provide
+alternative
+representations
+through
+server-driven
+content
+negotiation,
+that
+is
+by
+honoring
+the
+request's
+Accept
+and
+Accept-Encoding
+headers
+and
+responding
+with
+the
+supported
+TD
+serialization
+and
+equivalent
+Content-Type
+and
+Content-Encoding
+headers.
+</span>
+In
+addition,
+following
+the
+process
+normatively
+defined
+in
+the
+WoT
+Thing
+Description
+1.1
+specification
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href= "#bib-wot-thing-description11" title= "Web of Things (WoT) Thing Description 1.1">
+wot-thing-description11
+</a>
+</cite>
+],
+an
+HTTP-based
+TD
+Server
+providing
+a
+<a href="#dfn-td" class= "internalDFN" data-link-type="dfn" id="ref-for-dfn-td-14">
+TD
+</a>
+may
+provide
+modified
+TDs
+or
+error
+responses
+using
+a
+different
+default
+language
+after
+server-driven
+content
+negotiation,
+that
+is
+by
+honoring
+the
+request's
+Accept-Language
+header.
+</p>
+<p>
+<span class="rfc2119-assertion" id= "exploration-server-http-head">
+An
+HTTP-based
+TD
+Server
+providing
+a
+<a href="#dfn-td" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-td-15">
+TD
+</a>
+<em class="rfc2119">
+MUST
+</em>
+respond
+to
+<code>
+HEAD
+</code>
+requests
+by
+returning
+only
+the
+headers
+equivalent
+to
+those
+returned
+by
+a
+<code>
+GET
+</code>
+request
+to
+the
+same
+endpoint.
+</span>
+This
+enables
+clients
+to
+retrieve
+HTTP
+headers
+such
+as
+the
+Content-Length
+in
+advance
+to
+know
+the
+size
+of
+the
+<a href= "#dfn-td" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-td-16">
+TD
+</a>
+(in
+bytes)
+and
+decide
+on
+an
+efficient
+query
+strategy.
+</p>
+<p>
+In
+constrained
+environments,
+a
+single
+<a href="#dfn-td" class= "internalDFN" data-link-type="dfn" id="ref-for-dfn-td-17">
+TD
+</a>
+may
+be
+too
+large
+to
+process
+for
+the
+server
+or
+clients.
+See
+<a href= "#perf-incremental-transfer" data-matched-text= "[[[#perf-incremental-transfer]]]" class="sec-ref">
+<bdi class= "secno">
+10.1
+</bdi>
+Incremental
+Transfer
+</a>
+for
+protocol-specific
+recommendations
+on
+incremental
+transfer
+of
+the
+requested
+payload.
+</p>
+<p>
+Error
+responses:
+</p>
+<ul>
+<li>
+401
+(Unauthorized):
+No
+authentication.
+</li>
+<li>
+403
+(Forbidden):
+Insufficient
+rights
+to
+the
+resource.
+</li>
+</ul>
+</dd>
+</dl>
+<dl>
+<dt>
+CoAP
+</dt>
+<dd>
+<p>
+<span class="rfc2119-assertion" id= "exploration-server-coap-method">
+A
+CoAP-based
+TD
+Server
+providing
+a
+<a href="#dfn-td" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-td-18">
+TD
+</a>
+<em class="rfc2119">
+MUST
+</em>
+serve
+that
+resource
+with
+a
+<code>
+GET
+</code>
+method.
+</span>
+<span class= "rfc2119-assertion" id="exploration-server-coap-resp">
+A
+successful
+response
+from
+a
+CoAP-based
+TD
+Server
+providing
+a
+<a href="#dfn-td" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-td-19">
+TD
+</a>
+<em class="rfc2119">
+MUST
+</em>
+have
+a
+2.05
+(Content)
+status,
+contain
+a
+Content-Format
+option
+with
+value
+50
+(
+<code>
+application/json
+</code>
+)
+or
+432
+(
+<code>
+application/td+json
+</code>
+),
+and
+the
+<a href="#dfn-td" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-td-20">
+TD
+</a>
+in
+the
+payload.
+</span>
+Content-Format
+432
+is
+preferred
+as
+it
+is
+more
+specific
+and
+implies
+Content-Format
+50.
+Note
+that
+the
+payload
+might
+be
+split
+over
+multiple
+message
+exchanges
+using
+block-wise
+transfer
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href="#bib-rfc7959" title= "Block-Wise Transfers in the Constrained Application Protocol (CoAP)">
+RFC7959
+</a>
+</cite>
+].
+<span class="rfc2119-assertion" id= "exploration-server-coap-alternate-content">
+A
+CoAP-based
+TD
+Server
+providing
+a
+<a href="#dfn-td" class="internalDFN" data-link-type= "dfn" id="ref-for-dfn-td-21">
+TD
+</a>
+<em class="rfc2119">
+MAY
+</em>
+provide
+alternative
+representations
+through
+server-driven
+content
+negotiation,
+that
+is
+by
+honouring
+the
+request's
+Accept
+option
+and
+responding
+with
+the
+supported
+<a href="#dfn-td" class="internalDFN" data-link-type="dfn" id="ref-for-dfn-td-22">
+TD
+</a>
+serialization
+and
+equivalent
+Content-Format
+option.
+</span>
+</p>
+<p>
+<span class="rfc2119-assertion" id= "exploration-server-coap-size2">
+A
+CoAP-based
+<a href="#dfn-td" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-td-23">
+TD
+</a>
+Server
+providing
+a
+<a href="#dfn-td" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-td-24">
+TD
+</a>
+<em class="rfc2119">
+SHOULD
+</em>
+respond
+to
+requests
+containing
+a
+Size2
+option
+by
+including
+the
+size
+estimate
+of
+the
+<a href="#dfn-td" class="internalDFN" data-link-type="dfn" id="ref-for-dfn-td-25">
+TD
+</a>
+in
+its
+next
+response.
+</span>
+This
+is
+relevant
+when
+obtaining
+a
+<a href= "#dfn-td" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-td-26">
+TD
+</a>
+using
+block-wise
+transfer
+and
+enables
+clients
+to
+abort
+the
+retrieval
+if
+the
+total
+payload
+size
+should
+be
+too
+large
+for
+them
+to
+process.
+</p>
+<p>
+In
+constrained
+environments,
+a
+single
+<a href="#dfn-td" class= "internalDFN" data-link-type="dfn" id="ref-for-dfn-td-27">
+TD
+</a>
+may
+be
+too
+large
+to
+process
+for
+the
+server
+or
+clients.
+See
+<a href= "#perf-incremental-transfer" data-matched-text= "[[[#perf-incremental-transfer]]]" class="sec-ref">
+<bdi class= "secno">
+10.1
+</bdi>
+Incremental
+Transfer
+</a>
+for
+protocol-specific
+recommendations
+on
+incremental
+transfer
+of
+the
+requested
+payload.
+</p>
+<p>
+Error
+responses:
+</p>
+<ul>
+<li>
+4.01
+(Unauthorized):
+No
+authentication.
+</li>
+<li>
+4.03
+(Forbidden):
+Insufficient
+rights
+to
+the
+resource.
+</li>
+</ul>
+</dd>
+</dl>
+</section>
+<section id="exploration-directory" class="normative">
+<div class="header-wrapper">
+<h3 id="x7-3-thing-description-directory">
+<bdi class= "secno">
+7.3
+</bdi>
+Thing
+Description
+Directory
+</h3>
+<a class="self-link" href="#exploration-directory" aria-label= "Permalink for Section 7.3">
+</a>
+</div>
+<p>
+A
+<a href="#dfn-wot-thing-description-directory" class= "internalDFN" data-link-type="dfn" id= "ref-for-dfn-wot-thing-description-directory-20">
+Thing
+Description
+Directory
+</a>
+(TDD
+or
+Directory
+for
+short)
+is
+a
+<a href= "#dfn-thing" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-thing-6">
+Thing
+</a>
+that
+provides
+a
+service
+to
+manage
+a
+set
+of
+TDs
+describing
+other
+Things.
+</p>
+<section id="exploration-directory-info" class="normative">
+<div class="header-wrapper">
+<h4 id="x7-3-1-information-model">
+<bdi class="secno">
+7.3.1
+</bdi>
+Information
+Model
+</h4>
+<a class="self-link" href="#exploration-directory-info" aria-label= "Permalink for Section 7.3.1">
+</a>
+</div>
+<p>
+As
+shown
+in
+<a href="#exploration-class-diagram" data-matched-text="[[[#exploration-class-diagram]]]" class= "fig-ref" title= "The high-level class diagram of the exploration mechanisms, depicting how Thing Description Servers and Thing Description Directories provide TDs. A Self-describing Thing is a special case of a Thing Description Server that is also a Thing. A Thing Description Directory acts as a Thing Description Server for each Thing Description it contains.">
+Figure
+<bdi class="">
+4
+</bdi>
+</a>,
+the
+<a href= "#dfn-wot-thing-description-directory" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-wot-thing-description-directory-21">
+Thing
+Description
+Directory
+</a>
+can
+contain
+zero
+or
+more
+<a href="#dfn-td" class= "internalDFN" data-link-type="dfn" id="ref-for-dfn-td-28">
+TDs
+</a>.
+For
+every
+TD,
+the
+directory
+maintains
+additional
+metadata
+for
+bookkeeping
+and
+search
+purposes.
+These
+are
+described
+in
+<a href= "#exploration-directory-registration-info" data-matched-text= "[[[#exploration-directory-registration-info]]]" class= "sec-ref">
+<bdi class="secno">
+7.3.1.1
+</bdi>
+Registration
+Information
+</a>
+and
+<a href="#exploration-directory-anonymous-td" data-matched-text="[[[#exploration-directory-anonymous-td]]]" class="sec-ref">
+<bdi class="secno">
+7.3.1.3
+</bdi>
+Anonymous
+TD
+Identifiers
+</a>.
+A
+<a href="#dfn-td" class="internalDFN" data-link-type="dfn" id="ref-for-dfn-td-29">
+TD
+</a>
+that
+embeds
+such
+additional
+metadata
+as
+part
+of
+the
+interaction
+with
+the
+directory
+is
+called
+an
+<a href="#dfn-wot-enriched-thing-description" class= "internalDFN" data-link-type="dfn" id= "ref-for-dfn-wot-enriched-thing-description-1">
+Enriched
+TD
+</a>.
+</p>
+<section id="exploration-directory-registration-info" class= "normative">
+<div class="header-wrapper">
+<h5 id="x7-3-1-1-registration-information">
+<bdi class= "secno">
+7.3.1.1
+</bdi>
+Registration
+Information
+</h5>
+<a class="self-link" href= "#exploration-directory-registration-info" aria-label= "Permalink for Section 7.3.1.1">
+</a>
+</div>
+<p>
+The
+ontology
+of
+a
+<a href="#dfn-td" class="internalDFN" data-link-type="dfn" id="ref-for-dfn-td-30">
+TD
+</a>
+in
+the
+Discovery
+context
+was
+introduced
+in
+<a href= "#discovery-class-diagram-ontology" data-matched-text= "[[[#discovery-class-diagram-ontology]]]" class="fig-ref" title= "The ontology of Thing Descriptions in the Discovery context.">
+Figure
+<bdi class="">
+5
+</bdi>
+</a>.
+The
+<code>
+RegistrationInformation
+</code>
+class
+is
+associated
+with
+<a href="#dfn-td" class="internalDFN" data-link-type="dfn" id="ref-for-dfn-td-31">
+TDs
+</a>
+that
+are
+stored
+in
+a
+directory.
+The
+following
+table
+lists
+the
+registration
+information
+attributes
+for
+use
+within
+<a href="#dfn-td" class= "internalDFN" data-link-type="dfn" id="ref-for-dfn-td-32">
+TDs
+</a>
+that
+embed
+or
+reference
+the
+Discovery
+context.
+Note
+that
+only
+an
+<a href="#dfn-wot-enriched-thing-description" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-wot-enriched-thing-description-2">
+Enriched
+TD
+</a>
+embeds
+the
+registration
+information.
+<span class= "rfc2119-assertion" id="tdd-context-injection">
+An
+<a href= "#dfn-wot-enriched-thing-description" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-wot-enriched-thing-description-3">
+Enriched
+TD
+</a>
+<em class="rfc2119">
+MUST
+</em>
+contain
+in
+its
+@context
+the
+URI
+<code>
+https://www.w3.org/2022/wot/discovery
+</code>.
+</span>
+In
+this
+table,
+client
+refers
+to
+the
+producer
+or
+consumer
+of
+a
+<a href= "#dfn-td" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-td-33">
+TD
+</a>
+and
+server
+refers
+to
+the
+<a href= "#dfn-wot-thing-description-directory" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-wot-thing-description-directory-22">
+Thing
+Description
+Directory
+</a>.
+</p>
+<p>
+<span class="rfc2119-assertion" id="tdd-absolute-time">
+Whenever
+an
+absolute
+time
+is
+expressed
+using
+<a href= "https://www.w3.org/TR/2012/REC-xmlschema11-2-20120405/#dateTime">
+dateTime
+</a>
+it
+<em class="rfc2119">
+MUST
+</em>
+be
+interpreted
+as
+date-time
+as
+specified
+in
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href= "#bib-rfc3339" title= "Date and Time on the Internet: Timestamps">
+RFC3339
+</a>
+</cite>
+].
+</span>
+Specifically,
+the
+timezone
+offset
+is
+not
+optional.
+</p>
+<div class="note" id="issue-container-generatedID">
+<div role="heading" class="ednote-title marker" id="h-ednote" aria-level="6">
+<span>
+Editor's
+note
+</span>
+<span class= "issue-label">:
+dateTime
+vs.
+date-time
+</span>
+</div>
+<p class="">
+We
+should
+update
+the
+ontology
+to
+only
+use
+date-time
+and
+RFC3339
+and
+not
+this
+odd
+combination
+of
+dateTime
+and
+date-time,
+but
+this
+should
+also
+be
+resolved
+in
+the
+TD
+specification.
+However,
+we
+would
+need
+a
+new
+SHACL
+shape
+with
+this
+additional
+restriction.
+</p>
+</div>
+<table class="def">
+<thead>
+<tr>
+<th>
+Vocabulary
+term
+</th>
+<th>
+Description
+</th>
+<th>
+Client
+Assignment
+</th>
+<th>
+Server
+Assignment
+</th>
+<th>
+Type
+</th>
+</tr>
+</thead>
+<tbody>
+<tr class="rfc2119-table-assertion" id= "tdd-registrationinfo-vocab-created">
+<td>
+<code>
+created
+</code>
+</td>
+<td>
+Provides
+the
+absolute
+time
+when
+the
+TD
+instance
+was
+created
+inside
+the
+directory.
+<p>
+This
+<em class="rfc2119">
+MAY
+</em>
+be
+set
+by
+the
+directory
+and
+returned
+to
+consumers.
+</p>
+</td>
+<td>
+read-only
+</td>
+<td>
+optional
+</td>
+<td>
+<a href= "https://www.w3.org/TR/2012/REC-xmlschema11-2-20120405/#dateTime">
+<code>
+dateTime
+</code>
+</a>
+</td>
+</tr>
+<tr class="rfc2119-table-assertion" id= "tdd-registrationinfo-vocab-modified">
+<td>
+<code>
+modified
+</code>
+</td>
+<td>
+Provides
+the
+absolute
+time
+when
+the
+TD
+instance
+was
+last
+modified
+inside
+the
+directory.
+<p>
+This
+<em class="rfc2119">
+MAY
+</em>
+be
+set
+by
+the
+directory
+and
+returned
+to
+consumers.
+</p>
+</td>
+<td>
+read-only
+</td>
+<td>
+optional
+</td>
+<td>
+<a href= "https://www.w3.org/TR/2012/REC-xmlschema11-2-20120405/#dateTime">
+<code>
+dateTime
+</code>
+</a>
+</td>
+</tr>
+<tr class="rfc2119-table-assertion" id= "tdd-registrationinfo-vocab-expires">
+<td>
+<code>
+expires
+</code>
+</td>
+<td>
+Provides
+the
+absolute
+time
+when
+the
+TD
+instance
+registration
+expires.
+<p>
+The
+producer
+<em class="rfc2119">
+MAY
+</em>
+set
+this
+to
+indicate
+the
+absolute
+expiry
+time
+during
+the
+registration.
+</p>
+<p>
+For
+servers
+that
+support
+expirable
+TDs:
+If
+<code>
+ttl
+</code>
+(relative
+expiry)
+is
+present,
+the
+server
+<em class= "rfc2119">
+MUST
+</em>
+ignore
+client
+assignments
+to
+<code>
+expires
+</code>
+and
+instead
+compute
+and
+set
+it
+internally.
+</p>
+</td>
+<td>
+optional
+</td>
+<td>
+optional
+</td>
+<td>
+<a href= "https://www.w3.org/TR/2012/REC-xmlschema11-2-20120405/#dateTime">
+<code>
+dateTime
+</code>
+</a>
+</td>
+</tr>
+<tr class="rfc2119-table-assertion" id= "tdd-registrationinfo-vocab-ttl">
+<td>
+<code>
+ttl
+</code>
+</td>
+<td>
+Time-to-live:
+relative
+amount
+of
+time
+in
+seconds
+from
+the
+registration
+time
+until
+when
+the
+TD
+instance
+registration
+expires.
+<p>
+The
+producer
+<em class="rfc2119">
+MAY
+</em>
+set
+this
+to
+indicate
+the
+relative
+expiry
+time
+during
+the
+registration.
+</p>
+<p>
+For
+servers
+that
+support
+expirable
+TDs:
+The
+server
+<em class= "rfc2119">
+MUST
+</em>
+use
+<code>
+ttl
+</code>
+to
+calculate
+the
+<code>
+expires
+</code>
+(absolute
+expiry)
+value.
+</p>
+</td>
+<td>
+optional
+</td>
+<td>
+read-only
+</td>
+<td>
+<code>
+number
+</code>
+</td>
+</tr>
+<tr class="rfc2119-table-assertion" id= "tdd-registrationinfo-vocab-retrieved">
+<td>
+<code>
+retrieved
+</code>
+</td>
+<td>
+The
+absolute
+time
+at
+which
+the
+TD
+was
+retrieved
+from
+the
+server.
+<p>
+This
+is
+useful
+for
+clients
+that
+intend
+to
+process
+other
+absolute
+timestamps
+but
+do
+not
+have
+an
+internal
+clock
+or
+other
+means
+of
+acquiring
+the
+current
+time.
+</p>
+</td>
+<td>
+read-only
+</td>
+<td>
+optional
+</td>
+<td>
+<a href= "https://www.w3.org/TR/2012/REC-xmlschema11-2-20120405/#dateTime">
+<code>
+dateTime
+</code>
+</a>
+</td>
+</tr>
+</tbody>
+</table>
+</section>
+<section id="exploration-directory-registration-expiry" class= "normative">
+<div class="header-wrapper">
+<h5 id="x7-3-1-2-registration-expiry">
+<bdi class= "secno">
+7.3.1.2
+</bdi>
+Registration
+Expiry
+</h5>
+<a class="self-link" href= "#exploration-directory-registration-expiry" aria-label= "Permalink for Section 7.3.1.2">
+</a>
+</div>
+Section
+<a href="#exploration-directory-registration-info" data-matched-text="[[[#exploration-directory-registration-info]]]" class="sec-ref">
+<bdi class="secno">
+7.3.1.1
+</bdi>
+Registration
+Information
+</a>
+introduces
+some
+attributes
+to
+specify
+and
+discover
+the
+expiry
+time
+of
+registered
+<a href="#dfn-td" class="internalDFN" data-link-type="dfn" id="ref-for-dfn-td-34">
+TDs
+</a>.
+<p>
+Producers
+can
+set
+the
+expiry
+time
+to
+inform
+the
+directory
+and
+other
+consumers
+about
+the
+validity
+of
+the
+TD
+registrations.
+The
+expiry
+is
+also
+a
+useful
+indicator
+to
+inform
+the
+consumers
+about
+expiry
+of
+dynamic
+<a href="#dfn-td" class="internalDFN" data-link-type="dfn" id="ref-for-dfn-td-35">
+TDs
+</a>,
+e.g.
+when
+changes
+to
+metadata
+such
+as
+geolocation
+or
+properties
+are
+expected
+to
+be
+valid
+for
+a
+limited
+period.
+Consumers
+may
+rely
+on
+the
+expiry
+time
+to
+know
+how
+long
+a
+retrieved
+<a href="#dfn-td" class= "internalDFN" data-link-type="dfn" id="ref-for-dfn-td-36">
+TD
+</a>
+will
+be
+valid
+and
+when
+they
+need
+to
+request
+a
+more
+recent
+one.
+Consumers
+who
+retrieve
+an
+expired
+TD
+may
+consider
+it
+as
+metadata
+of
+an
+inactive
+client.
+</p>
+<p>
+For
+the
+servers,
+the
+expiry
+time
+is
+useful
+for
+implementing
+automatic
+removal
+of
+obsolete
+or
+accidental
+registrations.
+<span class="rfc2119-assertion" id= "tdd-registrationinfo-expiry-purge">
+Servers
+<em class= "rfc2119">
+SHOULD
+</em>
+periodically
+purge
+TDs
+that
+are
+past
+their
+expiry
+times.
+</span>
+Prescribing
+a
+global
+mandate
+or
+upper
+limit
+for
+the
+expiry
+time
+is
+application-specific
+and
+beyond
+the
+scope
+of
+this
+specification.
+Servers
+may
+mandate
+or
+set
+a
+configurable
+upper
+limit
+to
+expiry
+times
+and
+refuse
+incompliant
+requests.
+The
+purging
+by
+servers
+is
+particularly
+beneficial
+when
+interacting
+with
+clients
+(e.g.
+IoT
+devices)
+that
+are
+unable
+to
+explicitly
+deregister
+their
+<a href="#dfn-td" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-td-37">
+TDs
+</a>.
+This
+could
+be
+due
+to
+protocol-specific
+limitations,
+failure,
+destruction,
+or
+ungraceful
+decommissioning.
+Such
+clients
+should
+set
+a
+reasonably
+short
+expiry
+time
+and
+periodically
+extend
+it
+during
+the
+normal
+operation.
+The
+expiry
+can
+be
+extended
+by
+updating
+the
+registration
+either
+fully
+or
+partially,
+including
+an
+update
+that
+makes
+no
+changes
+to
+the
+TD;
+see
+<a href= "#exploration-directory-api-things-update" data-matched-text= "[[[#exploration-directory-api-things-update]]]" class= "sec-ref">
+<bdi class="secno">
+7.3.2.1.3
+</bdi>
+Update
+</a>.
+If
+a
+client
+ceases
+to
+operate,
+a
+directory
+with
+purging
+capability
+will
+automatically
+remove
+its
+registration.
+</p>
+</section>
+<section id="exploration-directory-anonymous-td" class="normative">
+<div class="header-wrapper">
+<h5 id="x7-3-1-3-anonymous-td-identifiers">
+<bdi class= "secno">
+7.3.1.3
+</bdi>
+Anonymous
+TD
+Identifiers
+</h5>
+<a class="self-link" href="#exploration-directory-anonymous-td" aria-label="Permalink for Section 7.3.1.3">
+</a>
+</div>
+The
+directory
+assigns
+local
+identifiers
+to
+<a href= "#dfn-wot-anonymous-thing-description" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-wot-anonymous-thing-description-1">
+Anonymous
+TDs
+</a>
+to
+enable
+management
+and
+retrieval
+of
+such
+TDs
+from
+the
+directory.
+<span class="rfc2119-assertion" id="tdd-anonymous-td-identifier">
+In
+situations
+where
+the
+server
+exposes
+an
+Anonymous
+TD
+(e.g.
+retrieval,
+listing,
+search),
+it
+<em class="rfc2119">
+MUST
+</em>
+add
+the
+local
+identifier
+as
+<code>
+id
+</code>
+of
+the
+TD
+to
+allow
+local
+referencing.
+</span>
+<span class="rfc2119-assertion" id= "tdd-anonymous-td-local-uuid">
+The
+local
+identifier
+<em class= "rfc2119">
+SHOULD
+</em>
+be
+a
+UUID
+Version
+4,
+presented
+as
+a
+URN
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href= "#bib-rfc4122" title= "A Universally Unique IDentifier (UUID) URN Namespace">
+RFC4122
+</a>
+</cite>
+].
+</span>
+UUID
+Version
+4
+is
+a
+random
+or
+pseudo-random
+number
+which
+does
+not
+carry
+unintended
+information
+about
+the
+host
+or
+the
+resource.
+</section>
+</section>
+<section id="exploration-directory-api" class="normative">
+<div class="header-wrapper">
+<h4 id="x7-3-2-directory-service-api">
+<bdi class= "secno">
+7.3.2
+</bdi>
+Directory
+Service
+API
+</h4>
+<a class="self-link" href="#exploration-directory-api" aria-label= "Permalink for Section 7.3.2">
+</a>
+</div>
+<p>
+Directory
+services
+provide
+access
+to
+<a href= "https://www.w3.org/TR/wot-security/#dfn-system-user-data">
+System
+User
+Data
+</a>
+and
+need
+to
+provide
+appropriate
+security
+and
+privacy
+protections.
+The
+use
+of
+secure
+transport
+protocols
+and
+access
+controls
+for
+authenticity
+and
+confidentiality
+in
+implementations
+of
+the
+WoT
+Directory
+Service
+API
+are
+governed
+by
+the
+Security
+Considerations
+and
+Privacy
+Considerations
+given
+in
+[
+<cite>
+<a class= "bibref" data-link-type="biblio" href="#bib-wot-architecture11" title= "Web of Things (WoT) Architecture 1.1">
+wot-architecture11
+</a>
+</cite>
+].
+</p>
+<p>
+The
+HTTP
+API
+responses
+must
+use
+appropriate
+status
+codes
+described
+in
+this
+section
+for
+success
+and
+error
+responses.
+<span class="rfc2119-assertion" id="tdd-http-error-response">
+The
+HTTP
+API
+<em class="rfc2119">
+MUST
+</em>
+use
+the
+Problem
+Details
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href= "#bib-rfc7807" title= "Problem Details for HTTP APIs">
+RFC7807
+</a>
+</cite>
+]
+format
+to
+carry
+error
+details
+in
+HTTP
+client
+error
+(4xx)
+and
+server
+error
+(5xx)
+responses.
+</span>
+This
+enables
+both
+machines
+and
+humans
+to
+know
+the
+high-level
+error
+class
+and
+fine-grained
+details.
+<span class= "rfc2119-assertion" id="tdd-http-error-response-utf-8">
+All
+HTTP
+API
+error
+responses
+described
+using
+Problem
+Details
+<em class= "rfc2119">
+MUST
+</em>
+be
+encoded
+using
+UTF-8.
+</span>
+<span class= "rfc2119-assertion" id="tdd-http-error-response-lang">
+HTTP
+API
+error
+responses
+<em class="rfc2119">
+MAY
+</em>
+report
+details
+in
+different
+languages
+using
+proactive
+negotiation,
+if
+the
+<code>
+Accept-Language
+</code>
+header
+field
+has
+been
+set
+in
+the
+HTTP
+request
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href= "#bib-rfc7231" title= "Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content">
+RFC7231
+</a>
+</cite>
+].
+</span>
+</p>
+<p>
+The
+APIs
+set
+the
+HTTP
+status
+codes
+as
+defined
+in
+Section
+6
+of
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href= "#bib-rfc7231" title= "Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content">
+RFC7231
+</a>
+</cite>
+].
+The
+list
+of
+used
+error
+codes
+include
+(but
+are
+not
+limited
+to)
+the
+following:
+</p>
+<ul>
+<li>
+400
+(Bad
+Request):
+Invalid
+client
+input
+in
+body,
+query,
+or
+headers.
+This
+is
+accompanied
+by
+an
+appropriate
+response
+message.
+</li>
+<li>
+401
+(Unauthorized):
+The
+request
+lacks
+valid
+authentication
+credentials.
+As
+noted
+in
+<a href="#exploration-secboot" data-matched-text="[[[#exploration-secboot]]]" class= "sec-ref">
+<bdi class="secno">
+7.1.2
+</bdi>
+Security
+Bootstrapping
+</a>,
+this
+is
+the
+first
+step
+in
+authentication
+negotiation,
+needed
+to
+bootstrap
+secure
+access
+to
+TDs.
+Information
+on
+what
+credentials
+are
+required
+will
+be
+included
+in
+a
+<code>
+WWW-Authenticate
+</code>
+header.
+</li>
+<li>
+403
+(Forbidden):
+Insufficient
+rights
+to
+access
+the
+resource.
+</li>
+<li>
+404
+(Not
+Found):
+TD
+or
+endpoint
+does
+not
+exist.
+This
+is
+accompanied
+by
+an
+appropriate
+response
+message.
+</li>
+</ul>
+<p>
+<span class="rfc2119-assertion" id="tdd-http-head">
+For
+each
+HTTP
+endpoint
+that
+responds
+to
+the
+<code>
+GET
+</code>
+method,
+the
+server
+<em class="rfc2119">
+MUST
+</em>
+accept
+<code>
+HEAD
+</code>
+requests
+and
+return
+only
+the
+headers.
+</span>
+This
+allows
+clients
+to
+retrieve
+headers
+such
+as
+the
+Content-Length
+without
+receiving
+the
+body
+and
+decide
+on
+a
+suitable
+strategy
+to
+query
+the
+information.
+For
+example,
+a
+constrained
+client
+can
+request
+only
+the
+necessary
+parts
+of
+an
+object
+(using
+an
+appropriate
+search
+query)
+or
+retrieve
+a
+list
+of
+items
+in
+small
+subsets.
+</p>
+<p>
+In
+constrained
+environments,
+a
+single
+TD
+may
+be
+too
+large
+to
+process
+for
+the
+server
+or
+clients.
+This
+affects
+both
+read
+(i.e.
+retrieving
+one
+or
+more
+TDs
+or
+TD
+fragments)
+and
+write
+(i.e.
+submitting
+a
+TD
+or
+Partial
+TD)
+operations.
+See
+<a href= "#perf-incremental-transfer" data-matched-text= "[[[#perf-incremental-transfer]]]" class="sec-ref">
+<bdi class= "secno">
+10.1
+</bdi>
+Incremental
+Transfer
+</a>
+for
+protocol-specific
+recommendations
+on
+incremental
+transfer
+of
+the
+payloads.
+</p>
+<p>
+To
+ensure
+the
+safe
+transmission
+of
+data
+over
+the
+URL,
+it
+is
+expected
+that
+both
+client
+and
+server
+percent
+encode/decode
+characters
+that
+conflict
+with
+delimiters
+in
+the
+rest
+of
+the
+URL.
+These
+characters
+are
+defined
+as
+<i>
+unsafe
+</i>
+in
+Section
+2.2
+of
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href= "#bib-rfc1738" title= "Uniform Resource Locators (URL)">
+RFC1738
+</a>
+</cite>
+].
+Unsafe
+characters
+can
+result
+in
+unexpected
+behavior
+if
+they
+appear
+in
+the
+URL,
+for
+example,
+when
+the
+resource
+ID
+included
+in
+the
+path
+is
+a
+URL
+by
+itself,
+or
+in
+the
+search
+query
+string.
+</p>
+<p>
+The
+directory
+APIs
+include
+mandatory,
+recommended,
+and
+optional
+features.
+<span class="rfc2119-assertion" id= "tdd-http-unsupported-feature">
+When
+a
+directory
+is
+unable
+to
+answer
+a
+request
+because
+of
+unsupported
+recommended
+or
+optional
+features,
+it
+<em class="rfc2119">
+SHOULD
+</em>
+inform
+the
+client
+about
+the
+absence
+of
+those
+features
+by
+returning
+appropriate
+HTTP
+errors.
+</span>
+The
+following
+examples
+can
+be
+used
+as
+guideline
+for
+implementations:
+</p>
+<ul>
+<li>
+If
+the
+missing
+feature
+is
+to
+customize
+functionality
+of
+an
+existing
+API
+use
+400
+(Bad
+Request)
+or
+501
+(Not
+Implemented).
+</li>
+<li>
+If
+an
+API
+endpoint
+is
+not
+provided
+(e.g.
+<code>
+/search/sparql
+</code>
+endpoint),
+use
+404
+(Not
+Found).
+</li>
+<li>
+If
+a
+method
+is
+not
+supported
+on
+an
+existing
+API
+endpoint
+(e.g.
+<code>
+PATCH
+</code>
+for
+<code>
+/things
+</code>
+endpoint),
+use
+405
+(Method
+Not
+Allowed).
+</li>
+</ul>
+<p>
+The
+process
+of
+modifying
+the
+default
+language
+of
+a
+TD
+using
+translations
+already
+provided
+in
+a
+TD
+is
+normatively
+described
+in
+the
+WoT
+Thing
+Description
+1.1
+specification
+[
+<cite>
+<a class= "bibref" data-link-type="biblio" href= "#bib-wot-thing-description11" title= "Web of Things (WoT) Thing Description 1.1">
+wot-thing-description11
+</a>
+</cite>
+].
+Using
+this
+process,
+a
+Directory
+server
+may
+provide
+modified
+TDs,
+or
+its
+own
+TD,
+using
+a
+different
+default
+language
+after
+server-driven
+content
+negotiation,
+that
+is
+by
+honouring
+the
+request's
+Accept-Language
+header.
+</p>
+<section id="exploration-directory-api-things" class="normative">
+<div class="header-wrapper">
+<h5 id="x7-3-2-1-things-api">
+<bdi class="secno">
+7.3.2.1
+</bdi>
+Things
+API
+</h5>
+<a class="self-link" href="#exploration-directory-api-things" aria-label="Permalink for Section 7.3.2.1">
+</a>
+</div>
+<p>
+The
+Things
+API
+is
+a
+RESTful
+HTTP
+API
+served
+at
+the
+<code>
+/things
+</code>
+endpoint
+providing
+interfaces
+to
+create,
+retrieve,
+update,
+delete,
+and
+list
+(CRUDL)
+<a href="#dfn-td" class= "internalDFN" data-link-type="dfn" id="ref-for-dfn-td-38">
+TDs
+</a>.
+The
+design
+of
+this
+API
+is
+in
+accordance
+with
+[
+<cite>
+<a class= "bibref" data-link-type="biblio" href="#bib-rfc7231" title= "Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content">
+RFC7231
+</a>
+</cite>
+]
+and
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href= "#bib-rest-iot" title= "RESTful Design for Internet of Things Systems">
+REST-IOT
+</a>
+</cite>
+].
+</p>
+<p>
+The
+HTTP
+API
+follows
+these
+general
+rules:
+</p>
+<ul>
+<li>
+<span class="rfc2119-assertion" id="tdd-things-list-only">
+The
+API
+<em class="rfc2119">
+MUST
+</em>
+provide
+the
+interface
+to
+list
+TDs.
+</span>
+The
+Search
+API
+allows
+filtering
+and
+selection
+from
+this
+list;
+see
+<a href="#exploration-directory-api-search" data-matched-text="[[[#exploration-directory-api-search]]]" class= "sec-ref">
+<bdi class="secno">
+7.3.2.3
+</bdi>
+Search
+API
+</a>.
+</li>
+<li>
+<span class="rfc2119-assertion" id="tdd-things-crud">
+The
+API
+<em class="rfc2119">
+MAY
+</em>
+provide
+the
+interfaces
+to
+create,
+read,
+update,
+and
+delete
+(CRUD)
+individual
+TDs.
+</span>
+</li>
+<li>
+A
+directory
+that
+provides
+both
+read
+and
+write
+over
+HTTP
+is
+considered
+a
+full
+HTTP
+directory.
+<span class="rfc2119-assertion" id="tdd-things-crudl">
+Full
+HTTP
+directories
+<em class= "rfc2119">
+SHOULD
+</em>
+implement
+all
+of
+CRUDL
+(create,
+read,
+update,
+delete,
+and
+list)
+interfaces.
+</span>
+It
+is
+practical
+to
+implement
+only
+the
+interfaces
+to
+read
+and
+list
+if
+the
+directory
+serves
+a
+static
+collection
+of
+<a href="#dfn-td" class="internalDFN" data-link-type="dfn" id="ref-for-dfn-td-39">
+TDs
+</a>.
+This
+is
+also
+useful
+for
+directories
+that
+intend
+to
+expose
+only
+retrieval
+operations
+over
+HTTP,
+and
+perform
+other
+operations
+via
+out-of-band
+mechanisms.
+<span class="rfc2119-assertion" id= "tdd-things-read-only-auth">
+To
+expose
+read-only
+access,
+the
+directory
+<em class="rfc2119">
+MUST
+</em>
+enforce
+access
+control
+on
+create,
+update,
+and
+delete
+interfaces.
+</span>
+</li>
+<li>
+<span class="rfc2119-assertion" id= "tdd-things-default-representation">
+The
+default
+serialization
+format
+for
+all
+request
+and
+success
+response
+bodies
+<em class= "rfc2119">
+MUST
+</em>
+be
+JSON,
+with
+JSON-LD
+1.1
+[
+<cite>
+<a class= "bibref" data-link-type="biblio" href="#bib-json-ld11" title= "JSON-LD 1.1">
+JSON-LD11
+</a>
+</cite>
+]
+syntax
+to
+support
+extensions
+and
+semantic
+processing.
+</span>
+</li>
+<li>
+<span class="rfc2119-assertion" id= "tdd-things-representation-alternate-input">
+Directories
+<em class= "rfc2119">
+MAY
+</em>
+accept
+alternative
+representations
+based
+on
+request's
+indicated
+Content-Type
+or
+Content-Encoding
+headers.
+</span>
+This
+is
+useful
+for
+applications
+that
+need
+to
+provide
+representations
+other
+than
+raw
+JSON
+as
+input
+to
+a
+directory.
+</li>
+<li>
+<span class="rfc2119-assertion" id= "tdd-http-representation-alternate-output">
+Directories
+<em class= "rfc2119">
+MAY
+</em>
+provide
+alternative
+representations
+through
+server-driven
+content
+negotiation,
+that
+is
+by
+honouring
+the
+request's
+Accept
+and
+Accept-Encoding
+headers
+and
+responding
+with
+the
+supported
+TD
+representation
+and
+equivalent
+Content-Type
+and
+Content-Encoding
+headers.
+</span>
+This
+is
+useful
+for
+applications
+that
+need
+to
+retrieve
+representations
+other
+than
+raw
+JSON
+from
+a
+directory,
+such
+as
+Gzip-compressed
+JSON.
+</li>
+</ul>
+<p>
+The
+CRUDL
+operations
+are
+described
+in
+the
+following
+sections:
+</p>
+<section id="exploration-directory-api-things-creation" class= "normative">
+<div class="header-wrapper">
+<h6 id="x7-3-2-1-1-creation">
+<bdi class="secno">
+7.3.2.1.1
+</bdi>
+Creation
+</h6>
+<a class="self-link" href= "#exploration-directory-api-things-creation" aria-label= "Permalink for Section 7.3.2.1.1">
+</a>
+</div>
+<p>
+Creation
+refers
+to
+the
+registration
+of
+a
+new
+<a href="#dfn-td" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-td-40">
+TD
+</a>
+inside
+the
+directory.
+</p>
+<p>
+The
+TD
+object
+is
+validated
+in
+accordance
+with
+<a href= "#exploration-directory-api-things-validation" data-matched-text= "[[[#exploration-directory-api-things-validation]]]" class= "sec-ref">
+<bdi class="secno">
+7.3.2.1.6
+</bdi>
+Validation
+</a>.
+Note
+that
+a
+TD
+may
+or
+may
+not
+be
+generated
+by
+the
+<a href="#dfn-thing" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-thing-7">
+Thing
+</a>
+it
+describes.
+For
+brownfield
+devices
+in
+particular
+a
+separate
+<a href="#dfn-wot-discoverer" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-wot-discoverer-2">
+Discoverer
+</a>
+process
+or
+service
+may
+be
+required
+that
+generates
+and
+registers
+a
+TD
+for
+a
+<a href= "#dfn-thing" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-thing-8">
+Thing
+</a>
+on
+its
+behalf.
+</p>
+<p>
+<span class="rfc2119-assertion" id= "tdd-things-create-known-vs-anonymous">
+A
+TD
+which
+is
+identified
+with
+an
+<code>
+id
+</code>
+attribute
+<em class="rfc2119">
+MUST
+</em>
+be
+handled
+differently
+with
+one
+that
+has
+no
+identifier
+(
+<a href= "#dfn-wot-anonymous-thing-description" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-wot-anonymous-thing-description-2">
+Anonymous
+TD
+</a>
+).
+</span>
+The
+create
+operations
+are
+elaborated
+below:
+</p>
+<ul>
+<li>
+<span class="rfc2119-assertion" id= "tdd-things-create-known-td">
+A
+TD
+that
+has
+an
+<code>
+id
+</code>
+<em class="rfc2119">
+MUST
+</em>
+be
+submitted
+to
+the
+directory
+in
+the
+body
+of
+an
+HTTP
+<code>
+PUT
+</code>
+request
+at
+<code>
+/things/{id}
+</code>
+endpoint,
+where
+<code>
+id
+</code>
+is
+the
+unique
+TD
+identifier,
+present
+inside
+the
+TD
+object.
+</span>
+An
+<a href="#dfn-wot-anonymous-thing-description" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-wot-anonymous-thing-description-3">
+Anonymous
+TD
+</a>
+is
+handled
+differently;
+see
+below.
+<span class="rfc2119-assertion" id= "tdd-things-create-known-contenttype">
+The
+request
+<em class= "rfc2119">
+SHOULD
+</em>
+contain
+<code>
+application/td+json
+</code>
+Content-Type
+header
+for
+JSON
+serialization
+of
+TD.
+</span>
+The
+TD
+object
+is
+validated
+in
+accordance
+with
+<a href= "#exploration-directory-api-things-validation" data-matched-text= "[[[#exploration-directory-api-things-validation]]]" class= "sec-ref">
+<bdi class="secno">
+7.3.2.1.6
+</bdi>
+Validation
+</a>.
+<span class="rfc2119-assertion" id= "tdd-things-create-known-td-resp">
+Upon
+successful
+processing,
+the
+server
+<em class="rfc2119">
+MUST
+</em>
+respond
+with
+201
+(Created)
+status.
+</span>
+<p>
+Note:
+If
+the
+target
+location
+corresponds
+to
+an
+existing
+TD,
+the
+request
+shall
+instead
+proceed
+as
+an
+Update
+operation
+and
+respond
+the
+appropriate
+status
+code
+(see
+Update
+section).
+</p>
+<p>
+The
+create
+operation
+for
+<a href="#dfn-td" class="internalDFN" data-link-type="dfn" id="ref-for-dfn-td-41">
+TDs
+</a>
+that
+have
+identifiers
+is
+specified
+as
+<code>
+createThing
+</code>
+action
+in
+<a href="#directory-api-spec" data-matched-text= "[[[#directory-api-spec]]]" class="sec-ref">
+<bdi class= "secno">
+7.3.2.4
+</bdi>
+API
+Specification
+(Thing
+Model)
+</a>.
+</p>
+</li>
+<li>
+<span class="rfc2119-assertion" id= "tdd-things-create-anonymous-td">
+An
+<a href= "#dfn-wot-anonymous-thing-description" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-wot-anonymous-thing-description-4">
+Anonymous
+TD
+</a>
+<em class="rfc2119">
+MUST
+</em>
+be
+submitted
+to
+the
+directory
+in
+the
+body
+of
+an
+HTTP
+<code>
+POST
+</code>
+request
+at
+<code>
+/things
+</code>
+endpoint.
+</span>
+<span class="rfc2119-assertion" id= "tdd-things-create-anonymous-contenttype">
+The
+request
+<em class= "rfc2119">
+SHOULD
+</em>
+contain
+<code>
+application/td+json
+</code>
+Content-Type
+header
+for
+JSON
+serialization
+of
+TD.
+</span>
+The
+TD
+object
+is
+validated
+in
+accordance
+with
+<a href= "#exploration-directory-api-things-validation" data-matched-text= "[[[#exploration-directory-api-things-validation]]]" class= "sec-ref">
+<bdi class="secno">
+7.3.2.1.6
+</bdi>
+Validation
+</a>.
+<span class="rfc2119-assertion" id= "tdd-things-create-anonymous-id">
+The
+directory
+<em class= "rfc2119">
+MUST
+</em>
+assign
+a
+local
+identifier
+to
+any
+<a href= "#dfn-wot-anonymous-thing-description" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-wot-anonymous-thing-description-5">
+Anonymous
+TD
+</a>
+to
+enable
+local
+management
+and
+retrieval
+from
+the
+directory.
+</span>
+The
+scheme
+of
+the
+system-generated
+ID
+is
+described
+in
+<a href= "#exploration-directory-anonymous-td" data-matched-text= "[[[#exploration-directory-anonymous-td]]]" class= "sec-ref">
+<bdi class="secno">
+7.3.1.3
+</bdi>
+Anonymous
+TD
+Identifiers
+</a>.
+<span class="rfc2119-assertion" id= "tdd-things-create-anonymous-td-resp">
+Upon
+successful
+processing,
+the
+server
+<em class="rfc2119">
+MUST
+</em>
+respond
+with
+201
+(Created)
+status
+and
+a
+Location
+header
+containing
+the
+system-generated
+URI
+of
+created
+TD
+resource.
+</span>
+The
+system-generated
+URI
+includes
+the
+system-generated
+identifier
+of
+the
+TD
+and
+can
+be
+used
+subsequently
+to
+query
+the
+TD
+from
+the
+directory.
+<p>
+The
+create
+operation
+for
+<a href= "#dfn-wot-anonymous-thing-description" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-wot-anonymous-thing-description-6">
+Anonymous
+TDs
+</a>
+is
+specified
+as
+<code>
+createAnonymousThing
+</code>
+action
+in
+<a href="#directory-api-spec" data-matched-text= "[[[#directory-api-spec]]]" class="sec-ref">
+<bdi class= "secno">
+7.3.2.4
+</bdi>
+API
+Specification
+(Thing
+Model)
+</a>.
+</p>
+</li>
+</ul>
+<p>
+A
+server
+that
+supports
+expirable
+TDs
+will
+realize
+such
+functionality
+as
+described
+in
+<a href= "#exploration-directory-registration-expiry" data-matched-text= "[[[#exploration-directory-registration-expiry]]]" class= "sec-ref">
+<bdi class="secno">
+7.3.1.2
+</bdi>
+Registration
+Expiry
+</a>.
+In
+particular,
+if
+<code>
+ttl
+</code>
+(relative
+expiry)
+is
+given
+during
+the
+creation,
+such
+servers
+will
+calculate
+and
+store
+the
+<code>
+expires
+</code>
+value.
+</p>
+</section>
+<section id="exploration-directory-api-things-retrieval" class= "normative">
+<div class="header-wrapper">
+<h6 id="x7-3-2-1-2-retrieval">
+<bdi class="secno">
+7.3.2.1.2
+</bdi>
+Retrieval
+</h6>
+<a class="self-link" href= "#exploration-directory-api-things-retrieval" aria-label= "Permalink for Section 7.3.2.1.2">
+</a>
+</div>
+<p>
+<span class="rfc2119-assertion" id="tdd-things-retrieve">
+The
+retrieval
+of
+an
+existing
+TD
+<em class="rfc2119">
+MUST
+</em>
+be
+done
+using
+an
+HTTP
+<code>
+GET
+</code>
+request
+at
+<code>
+/things/{id}
+</code>
+endpoint,
+where
+<code>
+id
+</code>
+is
+the
+unique
+TD
+identifier.
+</span>
+<span class="rfc2119-assertion" id="tdd-things-retrieve-resp">
+A
+successful
+response
+<em class="rfc2119">
+MUST
+</em>
+have
+200
+(OK)
+status
+and
+the
+requested
+TD
+in
+the
+body.
+</span>
+<span class= "rfc2119-assertion" id="tdd-things-retrieve-resp-content-type">
+A
+successful
+response
+with
+JSON
+serialization
+<em class= "rfc2119">
+MUST
+</em>
+contain
+either
+<code>
+application/json
+</code>
+or
+<code>
+application/td+json
+</code>
+in
+the
+Content-Type
+header.
+</span>
+Here
+<code>
+application/td+json
+</code>
+is
+preferred
+as
+it
+is
+more
+specific
+and
+implies
+<code>
+application/json
+</code>.
+Note
+that
+the
+default
+serialization
+is
+JSON
+with
+JSON-LD
+syntax,
+and
+alternative
+serializations
+can
+be
+negotiated;
+see
+<a href= "#exploration-directory-api-things" data-matched-text= "[[[#exploration-directory-api-things]]]" class= "sec-ref">
+<bdi class="secno">
+7.3.2.1
+</bdi>
+Things
+API
+</a>.
+</p>
+<p>
+The
+retrieve
+operation
+is
+specified
+as
+<code>
+retrieveThing
+</code>
+action
+in
+<a href="#directory-api-spec" data-matched-text="[[[#directory-api-spec]]]" class= "sec-ref">
+<bdi class="secno">
+7.3.2.4
+</bdi>
+API
+Specification
+(Thing
+Model)
+</a>.
+</p>
+<p>
+The
+following
+is
+an
+example
+of
+a
+retrieved
+TD:
+</p>
+<aside class="example" id="example-enriched-td">
+<div class="marker">
+<a class="self-link" href= "#example-enriched-td">
+Example
+<bdi>
+4
+</bdi>
+</a>
+<span class= "example-title">:
+Example
+Enriched
+TD
+</span>
+</div>
+<pre aria-busy="false"><code class="hljs json">{
+    <span class="hljs-attr">"@context"</span>: [
+        <span class=
+"hljs-string">"https://www.w3.org/2022/wot/td/v1.1"</span>,
+        <span class=
+"hljs-string">"https://www.w3.org/2022/wot/discovery"</span>
+    ],
+    <span class="hljs-attr">"id"</span>: <span class=
+"hljs-string">"urn:example:simple-td"</span>,
+    <span class="hljs-attr">"security"</span>: <span class=
+"hljs-string">"basic_sc"</span>,
+    <span class="hljs-attr">"securityDefinitions"</span>: {
+        <span class="hljs-attr">"basic_sc"</span>: {
+            <span class="hljs-attr">"scheme"</span>: <span class=
+"hljs-string">"basic"</span>
+        }
+    },
+    <span class="hljs-attr">"registration"</span>: {
+        <span class="hljs-attr">"created"</span>: <span class=
+"hljs-string">"2021-01-19T17:02:00Z"</span>,
+        <span class="hljs-attr">"modified"</span>: <span class=
+"hljs-string">"2021-01-19T17:02:00Z"</span>
+    },
+    <span class="hljs-attr">"title"</span>: <span class=
+"hljs-string">"Simple TD"</span>
+}
+</code>
+</pre>
+</aside>
+<p>
+This
+is
+an
+<a href="#dfn-wot-enriched-thing-description" class= "internalDFN" data-link-type="dfn" id= "ref-for-dfn-wot-enriched-thing-description-4">
+Enriched
+TD
+</a>
+which
+includes
+the
+registration
+information
+such
+as
+the
+creation
+and
+modification
+time
+of
+the
+TD
+within
+the
+directory.
+</p>
+<p>
+The
+example
+below
+shows
+a
+retrieved
+<a href= "#dfn-wot-anonymous-thing-description" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-wot-anonymous-thing-description-7">
+Anonymous
+TD
+</a>
+that
+is
+in
+<a href="#dfn-wot-enriched-thing-description" class= "internalDFN" data-link-type="dfn" id= "ref-for-dfn-wot-enriched-thing-description-5">
+Enriched
+TD
+</a>
+form
+and
+has
+local
+identifier
+<code>
+urn:uuid:48951ff3-4019-4e67-b217-dbbf011873dc
+</code>.
+</p>
+<aside class="example" id="example-anonymous-enriched-td">
+<div class="marker">
+<a class="self-link" href= "#example-anonymous-enriched-td">
+Example
+<bdi>
+5
+</bdi>
+</a>
+<span class="example-title">:
+Example
+Enriched
+Anonymous
+TD
+</span>
+</div>
+<pre aria-busy="false"><code class="hljs json">{
+    <span class="hljs-attr">"@context"</span>: [
+        <span class=
+"hljs-string">"https://www.w3.org/2022/wot/td/v1.1"</span>,
+        <span class=
+"hljs-string">"https://www.w3.org/2022/wot/discovery"</span>
+    ],
+    <span class="hljs-attr">"id"</span>: <span class=
+"hljs-string">"urn:uuid:48951ff3-4019-4e67-b217-dbbf011873dc"</span>,
+    <span class="hljs-attr">"security"</span>: <span class=
+"hljs-string">"basic_sc"</span>,
+    <span class="hljs-attr">"securityDefinitions"</span>: {
+        <span class="hljs-attr">"basic_sc"</span>: {
+            <span class="hljs-attr">"scheme"</span>: <span class=
+"hljs-string">"basic"</span>
+        }
+    },
+    <span class="hljs-attr">"registration"</span>: {
+        <span class="hljs-attr">"created"</span>: <span class=
+"hljs-string">"2021-01-19T17:02:00Z"</span>,
+        <span class="hljs-attr">"modified"</span>: <span class=
+"hljs-string">"2021-01-19T17:02:00Z"</span>
+    },
+    <span class="hljs-attr">"title"</span>: <span class=
+"hljs-string">"Anonymous TD"</span>
+}
+</code>
+</pre>
+</aside>
+<p>
+The
+following
+is
+an
+example
+of
+a
+retrieved
+TD
+that
+was
+registered
+with
+a
+relative
+expiry
+time
+of
+3600
+seconds
+(one
+hour).
+The
+server
+has
+calculated
+the
+absolute
+expiry
+time
+as
+one
+hour
+after
+the
+modification
+time.
+</p>
+<aside class="example" id="example-expirable-enriched-td">
+<div class="marker">
+<a class="self-link" href= "#example-expirable-enriched-td">
+Example
+<bdi>
+6
+</bdi>
+</a>
+<span class="example-title">:
+Example
+Expirable
+Enriched
+TD
+</span>
+</div>
+<pre aria-busy="false"><code class="hljs json">{
+    <span class="hljs-attr">"@context"</span>: [
+        <span class=
+"hljs-string">"https://www.w3.org/2022/wot/td/v1.1"</span>,
+        <span class=
+"hljs-string">"https://www.w3.org/2022/wot/discovery"</span>
+    ],
+    <span class="hljs-attr">"id"</span>: <span class=
+"hljs-string">"urn:example:expirable-td"</span>,
+    <span class="hljs-attr">"security"</span>: <span class=
+"hljs-string">"basic_sc"</span>,
+    <span class="hljs-attr">"securityDefinitions"</span>: {
+        <span class="hljs-attr">"basic_sc"</span>: {
+            <span class="hljs-attr">"scheme"</span>: <span class=
+"hljs-string">"basic"</span>
+        }
+    },
+    <span class="hljs-attr">"registration"</span>: {
+        <span class="hljs-attr">"created"</span>: <span class=
+"hljs-string">"2021-05-10T16:00:00Z"</span>,
+        <span class="hljs-attr">"modified"</span>: <span class=
+"hljs-string">"2021-05-10T17:00:00Z"</span>,
+        <span class="hljs-attr">"expires"</span>: <span class=
+"hljs-string">"2021-05-10T18:00:00Z"</span>,
+        <span class="hljs-attr">"ttl"</span>: <span class=
+"hljs-number">3600</span>,
+        <span class="hljs-attr">"retrieved"</span>: <span class=
+"hljs-string">"2021-05-10T17:35:00Z"</span>
+    },
+    <span class="hljs-attr">"title"</span>: <span class=
+"hljs-string">"Expirable TD"</span>
+}
+</code>
+</pre>
+</aside>
+<p>
+For
+the
+sake
+of
+readability,
+the
+time
+values
+in
+this
+example
+are
+set
+to
+exact
+numbers.
+In
+realistic
+settings,
+time
+values
+may
+include
+fractions.
+</p>
+</section>
+<section id="exploration-directory-api-things-update" class= "normative">
+<div class="header-wrapper">
+<h6 id="x7-3-2-1-3-update">
+<bdi class="secno">
+7.3.2.1.3
+</bdi>
+Update
+</h6>
+<a class="self-link" href= "#exploration-directory-api-things-update" aria-label= "Permalink for Section 7.3.2.1.3">
+</a>
+</div>
+<p>
+The
+update
+operations
+are
+to
+replace
+or
+partially
+modify
+an
+existing
+TD.
+</p>
+<p>
+The
+update
+operations
+are
+described
+below:
+</p>
+<ul>
+<li>
+<span class="rfc2119-assertion" id="tdd-things-update">
+A
+modified
+TD
+<em class="rfc2119">
+MUST
+</em>
+replace
+an
+existing
+one
+when
+submitted
+using
+an
+HTTP
+<code>
+PUT
+</code>
+request
+at
+<code>
+/things/{id}
+</code>
+endpoint,
+where
+<code>
+id
+</code>
+is
+the
+identifier
+of
+the
+existing
+TD.
+</span>
+<span class= "rfc2119-assertion" id="tdd-things-update-contenttype">
+The
+request
+<em class="rfc2119">
+SHOULD
+</em>
+contain
+<code>
+application/td+json
+</code>
+Content-Type
+header
+for
+JSON
+serialization
+of
+TD.
+</span>
+The
+TD
+object
+is
+validated
+in
+accordance
+with
+<a href= "#exploration-directory-api-things-validation" data-matched-text= "[[[#exploration-directory-api-things-validation]]]" class= "sec-ref">
+<bdi class="secno">
+7.3.2.1.6
+</bdi>
+Validation
+</a>.
+<span class="rfc2119-assertion" id="tdd-things-update-resp">
+Upon
+success,
+the
+server
+<em class="rfc2119">
+MUST
+</em>
+respond
+with
+204
+(No
+Content)
+status.
+</span>
+<p>
+This
+operation
+is
+specified
+as
+<code>
+updateThing
+</code>
+property
+in
+<a href="#directory-api-spec" data-matched-text= "[[[#directory-api-spec]]]" class="sec-ref">
+<bdi class= "secno">
+7.3.2.4
+</bdi>
+API
+Specification
+(Thing
+Model)
+</a>.
+</p>
+<p>
+A
+server
+that
+supports
+expirable
+TDs
+will
+realize
+such
+functionality
+as
+described
+in
+<a href= "#exploration-directory-registration-expiry" data-matched-text= "[[[#exploration-directory-registration-expiry]]]" class= "sec-ref">
+<bdi class="secno">
+7.3.1.2
+</bdi>
+Registration
+Expiry
+</a>.
+If
+<code>
+ttl
+</code>
+(relative
+expiry)
+is
+set
+during
+the
+update
+operation,
+the
+server
+will
+calculate
+and
+set
+the
+<code>
+expires
+</code>
+(absolute
+expiry)
+value.
+</p>
+<p>
+Note:
+If
+the
+target
+location
+does
+not
+correspond
+to
+an
+existing
+TD,
+the
+request
+shall
+instead
+proceed
+as
+a
+Create
+operation
+and
+respond
+the
+appropriate
+status
+code
+(see
+Create
+section).
+In
+other
+words,
+an
+HTTP
+<code>
+PUT
+</code>
+request
+acts
+as
+a
+create
+or
+update
+operation.
+</p>
+</li>
+<li>
+<span class="rfc2119-assertion" id= "tdd-things-update-partial">
+An
+existing
+TD
+<em class= "rfc2119">
+MUST
+</em>
+be
+partially
+modified
+when
+the
+modified
+parts
+are
+submitted
+using
+an
+HTTP
+<code>
+PATCH
+</code>
+request
+at
+<code>
+/things/{id}
+</code>
+endpoint,
+where
+<code>
+id
+</code>
+is
+the
+identifier
+of
+the
+existing
+TD.
+</span>
+<span class= "rfc2119-assertion" id="tdd-things-update-partial-mergepatch">
+The
+partial
+update
+<em class="rfc2119">
+MUST
+</em>
+be
+processed
+using
+the
+JSON
+merge
+patch
+format
+described
+in
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href="#bib-rfc7396" title= "JSON Merge Patch">
+RFC7396
+</a>
+</cite>
+].
+</span>
+<span class= "rfc2119-assertion" id="tdd-things-update-partial-contenttype">
+The
+request
+<em class="rfc2119">
+MUST
+</em>
+contain
+<code>
+application/merge-patch+json
+</code>
+Content-Type
+header
+for
+JSON
+serialization
+of
+the
+merge
+patch
+document.
+</span>
+<span class= "rfc2119-assertion" id="tdd-things-update-partial-partialtd">
+The
+input
+<em class="rfc2119">
+MUST
+</em>
+be
+in
+<a href= "#dfn-wot-partial-thing-description" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-wot-partial-thing-description-1">
+Partial
+TD
+</a>
+form
+and
+conform
+to
+the
+original
+TD
+structure.
+</span>
+If
+the
+input
+contains
+members
+that
+appear
+in
+the
+original
+TD,
+their
+values
+are
+replaced.
+If
+a
+member
+does
+not
+appear
+in
+the
+original
+TD,
+that
+member
+is
+added.
+If
+the
+member
+is
+set
+to
+<code>
+null
+</code>
+but
+appear
+in
+the
+original
+TD,
+that
+member
+is
+removed.
+Members
+with
+object
+values
+are
+processed
+recursively.
+After
+applying
+the
+modifications,
+the
+TD
+object
+is
+validated
+in
+accordance
+with
+<a href="#exploration-directory-api-things-validation" data-matched-text= "[[[#exploration-directory-api-things-validation]]]" class= "sec-ref">
+<bdi class="secno">
+7.3.2.1.6
+</bdi>
+Validation
+</a>.
+<span class="rfc2119-assertion" id= "tdd-things-update-partial-resp">
+Upon
+success,
+the
+server
+<em class="rfc2119">
+MUST
+</em>
+respond
+with
+a
+204
+(No
+Content)
+status.
+</span>
+<p>
+This
+operation
+is
+specified
+as
+<code>
+partiallyUpdateThing
+</code>
+property
+in
+<a href="#directory-api-spec" data-matched-text= "[[[#directory-api-spec]]]" class="sec-ref">
+<bdi class= "secno">
+7.3.2.4
+</bdi>
+API
+Specification
+(Thing
+Model)
+</a>.
+</p>
+<p>
+A
+server
+that
+supports
+expirable
+TDs
+will
+realize
+such
+functionality
+as
+described
+in
+<a href= "#exploration-directory-registration-expiry" data-matched-text= "[[[#exploration-directory-registration-expiry]]]" class= "sec-ref">
+<bdi class="secno">
+7.3.1.2
+</bdi>
+Registration
+Expiry
+</a>.
+During
+the
+partial
+update
+operation,
+if
+the
+resulting
+<a href= "#dfn-td" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-td-42">
+TD
+</a>
+has
+<code>
+ttl
+</code>
+(relative
+expiry),
+the
+server
+will
+calculate
+and
+set
+a
+new
+<code>
+expires
+</code>
+(absolute
+expiry)
+value.
+</p>
+<p>
+A
+patch
+operation
+is
+particularly
+useful
+to
+efficiently
+extend
+the
+expiry
+of
+a
+registration
+that
+uses
+a
+<code>
+ttl
+</code>
+(relative
+expiry)
+value.
+This
+is
+typically
+done
+by
+submitting
+an
+empty
+merge
+patch
+document,
+i.e.
+an
+empty
+JSON
+object.
+This
+effectively
+translates
+to
+performing
+a
+partial
+update
+operation
+that
+updates
+nothing,
+but
+triggers
+the
+recalculation
+of
+<code>
+expires
+</code>
+(absolute
+expiry)
+value.
+This
+expiry
+functionality
+only
+works
+if
+the
+server
+supports
+it
+as
+defined
+in
+<a href= "#exploration-directory-registration-expiry" data-matched-text= "[[[#exploration-directory-registration-expiry]]]" class= "sec-ref">
+<bdi class="secno">
+7.3.1.2
+</bdi>
+Registration
+Expiry
+</a>.
+</p>
+<p>
+The
+following
+example
+is
+a
+merge
+patch
+document
+to
+update
+only
+the
+<code>
+base
+</code>
+and
+registration
+<code>
+expires
+</code>
+fields
+of
+a
+TD:
+</p>
+<aside class="example" id="example-patch-enriched-td">
+<div class="marker">
+<a class="self-link" href= "#example-patch-enriched-td">
+Example
+<bdi>
+7
+</bdi>
+</a>
+<span class= "example-title">:
+Example
+merge
+patch
+document
+</span>
+</div>
+<pre aria-busy="false"><code class="hljs json">{
+    <span class="hljs-attr">"base"</span>: <span class=
+"hljs-string">"http://192.168.0.2/"</span>,
+    <span class="hljs-attr">"registration"</span>: {
+        <span class="hljs-attr">"expires"</span>: <span class=
+"hljs-string">"2021-01-20T17:02:00Z"</span>
+    }
+}
+</code>
+</pre>
+This
+is
+a
+valid
+way
+of
+extending
+the
+absolute
+expiry
+only
+if
+the
+stored
+TD
+has
+no
+<code>
+ttl
+</code>
+(relative
+expiry).
+For
+more
+details,
+refer
+to
+<a href= "#exploration-directory-registration-expiry" data-matched-text= "[[[#exploration-directory-registration-expiry]]]" class= "sec-ref">
+<bdi class="secno">
+7.3.1.2
+</bdi>
+Registration
+Expiry
+</a>.
+</aside>
+</li>
+</ul>
+</section>
+<section id="exploration-directory-api-things-deletion" class= "normative">
+<div class="header-wrapper">
+<h6 id="x7-3-2-1-4-deletion">
+<bdi class="secno">
+7.3.2.1.4
+</bdi>
+Deletion
+</h6>
+<a class="self-link" href= "#exploration-directory-api-things-deletion" aria-label= "Permalink for Section 7.3.2.1.4">
+</a>
+</div>
+<p>
+<span class="rfc2119-assertion" id="tdd-things-delete">
+A
+delete
+operation
+<em class="rfc2119">
+MUST
+</em>
+be
+done
+using
+an
+HTTP
+<code>
+DELETE
+</code>
+request
+at
+<code>
+/things/{id}
+</code>,
+where
+<code>
+id
+</code>
+is
+the
+identifier
+of
+the
+existing
+TD.
+</span>
+<span class="rfc2119-assertion" id="tdd-things-delete-resp">
+A
+successful
+response
+<em class="rfc2119">
+MUST
+</em>
+have
+204
+(No
+Content)
+status.
+</span>
+The
+retrieve
+operation
+is
+specified
+as
+<code>
+deleteThing
+</code>
+property
+in
+<a href="#directory-api-spec" data-matched-text="[[[#directory-api-spec]]]" class= "sec-ref">
+<bdi class="secno">
+7.3.2.4
+</bdi>
+API
+Specification
+(Thing
+Model)
+</a>.
+</p>
+</section>
+<section id="exploration-directory-api-things-listing" class= "normative">
+<div class="header-wrapper">
+<h6 id="x7-3-2-1-5-listing">
+<bdi class="secno">
+7.3.2.1.5
+</bdi>
+Listing
+</h6>
+<a class="self-link" href= "#exploration-directory-api-things-listing" aria-label= "Permalink for Section 7.3.2.1.5">
+</a>
+</div>
+<p>
+The
+listing
+endpoint
+provides
+different
+ways
+to
+query
+the
+collection
+of
+full
+TD
+objects
+from
+the
+directory.
+</p>
+<p>
+In
+many
+scenarios,
+retrieving
+parts
+instead
+of
+full
+TD
+objects
+is
+preferred
+because
+only
+a
+subset
+of
+elements
+are
+needed
+(e.g.
+<code>
+id
+</code>
+and
+<code>
+href
+</code>
+of
+a
+property
+for
+all
+TDs)
+and
+to
+save
+networking
+resources.
+The
+Search
+API
+allows
+querying
+parts
+of
+TD
+objects;
+see
+<a href= "#exploration-directory-api-search" data-matched-text= "[[[#exploration-directory-api-search]]]" class= "sec-ref">
+<bdi class="secno">
+7.3.2.3
+</bdi>
+Search
+API
+</a>.
+</p>
+<p>
+<span class="rfc2119-assertion" id="tdd-things-list-method">
+The
+directory
+<em class="rfc2119">
+MUST
+</em>
+allow
+retrieval
+of
+existing
+TDs
+using
+HTTP
+<code>
+GET
+</code>
+requests
+at
+the
+<code>
+/things
+</code>
+endpoint.
+</span>
+<span class= "rfc2119-assertion" id="tdd-things-list-resp">
+A
+successful
+response
+<em class="rfc2119">
+MUST
+</em>
+have
+200
+(OK)
+status
+and
+an
+array
+of
+TDs
+in
+the
+body.
+</span>
+<span class="rfc2119-assertion" id= "tdd-things-list-resp-content-type">
+A
+successful
+response
+with
+JSON
+serialization
+<em class="rfc2119">
+MUST
+</em>
+contain
+either
+<code>
+application/json
+</code>
+or
+<code>
+application/ld+json
+</code>
+in
+the
+Content-Type
+header.
+</span>
+Here
+<code>
+application/ld+json
+</code>
+is
+preferred
+as
+it
+is
+more
+specific
+and
+implies
+<code>
+application/json
+</code>.
+Note
+that
+the
+default
+serialization
+is
+JSON
+with
+JSON-LD
+syntax,
+and
+alternative
+serializations
+can
+be
+negotiated;
+see
+<a href= "#exploration-directory-api-things" data-matched-text= "[[[#exploration-directory-api-things]]]" class= "sec-ref">
+<bdi class="secno">
+7.3.2.1
+</bdi>
+Things
+API
+</a>.
+</p>
+<p>
+There
+may
+be
+scenarios
+in
+which
+clients
+need
+to
+retrieve
+the
+collection
+in
+small
+subsets
+of
+TDs.
+While
+the
+Search
+API
+(
+<a href= "#exploration-directory-api-search" data-matched-text= "[[[#exploration-directory-api-search]]]" class= "sec-ref">
+<bdi class="secno">
+7.3.2.3
+</bdi>
+Search
+API
+</a>
+)
+does
+offer
+the
+ability
+to
+query
+a
+specific
+range,
+it
+may
+not
+be
+optimal,
+nor
+developer-friendly.
+<span class="rfc2119-assertion" id= "tdd-things-list-pagination">
+The
+server
+<em class= "rfc2119">
+MAY
+</em>
+support
+pagination
+to
+return
+the
+collection
+in
+small
+subsets.
+</span>
+The
+pagination
+must
+be
+based
+on
+the
+following
+rules:
+</p>
+<ul>
+<li>
+<span class="rfc2119-assertion" id= "tdd-things-list-pagination-limit">
+When
+the
+<code>
+limit
+</code>
+query
+parameter
+is
+set
+to
+a
+positive
+integer,
+the
+server
+<em class= "rfc2119">
+MAY
+</em>
+respond
+with
+a
+subset
+of
+TDs
+totalling
+to
+less
+than
+or
+equal
+to
+the
+requested
+number.
+</span>
+</li>
+<li>
+<span class="rfc2119-assertion" id= "tdd-things-list-pagination-header-nextlink">
+When
+there
+are
+more
+TDs
+after
+a
+returned
+subset
+of
+the
+collection,
+the
+response
+<em class="rfc2119">
+MUST
+</em>
+contain
+a
+<code>
+next
+</code>
+Link
+header
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href= "#bib-rfc8288" title="Web Linking">
+RFC8288
+</a>
+</cite>
+]
+with
+the
+URL
+of
+the
+next
+subset.
+</span>
+<span class="rfc2119-assertion" id= "tdd-things-list-pagination-header-nextlink-attr">
+The
+<code>
+next
+</code>
+link
+<em class="rfc2119">
+MUST
+</em>
+include
+all
+arguments
+needed
+to
+produce
+the
+same
+set
+of
+data
+and
+its
+ordering,
+in
+particular
+the
+same
+<code>
+limit
+</code>
+argument
+given
+on
+the
+initial
+request
+as
+well
+as
+a
+zero-based
+<code>
+offset
+</code>
+argument
+anchored
+at
+the
+beginning
+of
+the
+next
+subset.
+</span>
+<span class="rfc2119-assertion" id= "tdd-things-list-pagination-header-nextlink-base">
+The
+link
+<em class="rfc2119">
+MUST
+</em>
+be
+absolute
+or
+relative
+to
+directory
+API's
+base
+URL.
+</span>
+Moreover,
+it
+may
+include
+additional
+arguments
+that
+are
+necessary
+for
+ordering
+or
+session
+management.
+</li>
+<li>
+<span class="rfc2119-assertion" id= "tdd-things-list-pagination-header-canonicallink">
+All
+paged
+responses
+<em class="rfc2119">
+MUST
+</em>
+contain
+a
+<code>
+canonical
+</code>
+Link
+header
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href="#bib-rfc8288" title= "Web Linking">
+RFC8288
+</a>
+</cite>
+]
+pointing
+to
+the
+collection
+and
+include
+an
+<code>
+etag
+</code>
+parameter
+to
+represent
+the
+current
+state
+of
+the
+collection.
+</span>
+The
+link
+may
+be
+absolute
+or
+relative
+to
+directory
+API's
+base
+URL.
+The
+<code>
+etag
+</code>
+value
+could
+be
+a
+revision
+number,
+timestamp,
+or
+UUID
+Version
+4,
+set
+whenever
+the
+TD
+collection
+changes
+in
+a
+way
+that
+affects
+the
+ordering
+of
+the
+TDs.
+The
+clients
+may
+rely
+on
+the
+<code>
+etag
+</code>
+value
+to
+know
+whether
+the
+collection
+remains
+consistent
+across
+paginated
+retrieval
+of
+the
+collection.
+For
+example,
+creation
+or
+deletion
+of
+TDs
+or
+update
+of
+TD
+fields
+used
+for
+ordering
+may
+shift
+the
+calculated
+paging
+window.
+</li>
+<li>
+<span class="rfc2119-assertion" id= "tdd-things-list-pagination-order-default">
+The
+collection
+<em class="rfc2119">
+MUST
+</em>
+be
+sorted
+in
+ascending
+order
+using
+Unicode
+code
+point
+order
+by
+the
+unique
+identifier
+of
+TDs.
+</span>
+</li>
+</ul>
+<p>
+This
+above
+specification
+follows
+a
+subset
+of
+Linked
+Data
+Paging
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href= "#bib-ldp-paging" title= "Linked Data Platform Paging 1.0">
+LDP-Paging
+</a>
+</cite>
+]
+to
+allow
+optional
+pagination
+of
+the
+JSON-LD
+array.
+Additional
+parts
+of
+Linked
+Data
+Paging
+may
+be
+implemented
+for
+examples
+to
+honour
+client's
+query
+preference
+or
+to
+add
+other
+link
+relations
+for
+semantic
+annotation
+and
+alternative
+navigation
+links.
+</p>
+<p>
+The
+following
+example
+provides
+a
+walk-through
+of
+the
+paginated
+retrieval
+of
+TDs:
+</p>
+<aside class="example" id="example-pagination">
+<div class="marker">
+<a class="self-link" href= "#example-pagination">
+Example
+<bdi>
+8
+</bdi>
+</a>
+<span class= "example-title">:
+Query
+all
+TDs
+with
+page
+size
+10.
+</span>
+</div>
+The
+client
+requests
+the
+list
+with
+a
+<code>
+limit
+</code>
+of
+10:
+<pre aria-busy="false"><code class=
+"hljs">GET /things?limit=10 HTTP/1.1   
+Host:
+tdd.example.com
+</code>
+</pre>
+Response:
+<pre aria-busy="false"><code class="hljs http"><span class=
+"hljs-meta">HTTP/1.1</span> <span class="hljs-number">200</span> OK
+<span class="hljs-attribute">Content-Type</span><span class=
+"hljs-punctuation">: </span>application/ld+json
+<span class="hljs-attribute">Link</span><span class=
+"hljs-punctuation">: </span>&lt;/things?offset=10&amp;limit=10&gt;; rel="next"
+<span class="hljs-attribute">Link</span><span class=
+"hljs-punctuation">: </span>&lt;/things&gt;; rel="canonical"; etag="v1"
+<span class="css"><span class=
+"hljs-selector-attr">
+[{
+TD
+},
+...9
+other
+TDs...
+]
+</span>
+</span>
+</code>
+</pre>
+The
+response
+includes
+two
+Link
+headers
+with
+relative
+URLs:
+<code>
+next
+</code>
+link
+to
+query
+the
+remaining
+TDs,
+<code>
+canonical
+</code>
+link
+referencing
+the
+full
+collection
+with
+<code>
+etag
+</code>
+value
+indicating
+the
+state
+of
+that
+collection.
+<br />
+The
+response
+body
+is
+an
+array
+of
+10
+TDs.
+<br />
+<br />
+The
+presence
+of
+the
+<code>
+next
+</code>
+link
+implies
+that
+subsequent
+pages
+should
+be
+queried
+for
+the
+remaining
+TDs.
+The
+client
+requests
+the
+next
+page
+via
+the
+<code>
+next
+</code>
+link:
+<pre aria-busy="false"><code class=
+"hljs">GET /things?offset=10&amp;limit=10 HTTP/1.1   
+Host:
+tdd.example.com
+</code>
+</pre>
+Response:
+<pre aria-busy="false"><code class="hljs http"><span class=
+"hljs-meta">HTTP/1.1</span> <span class="hljs-number">200</span> OK
+<span class="hljs-attribute">Content-Type</span><span class=
+"hljs-punctuation">: </span>application/ld+json
+<span class="hljs-attribute">Link</span><span class=
+"hljs-punctuation">: </span>&lt;/things&gt;; rel="canonical"; etag="v1"
+<span class="css"><span class=
+"hljs-selector-attr">
+[{
+TD
+},
+{
+TD
+}]
+</span>
+</span>
+</code>
+</pre>
+The
+server
+response
+has
+the
+remaining
+two
+TDs.
+There
+is
+no
+<code>
+next
+</code>
+link,
+because
+this
+is
+the
+last
+page.
+The
+<code>
+etag
+</code>
+value
+has
+not
+changed
+implying
+that
+the
+collection
+has
+remained
+consistent
+between
+the
+two
+requests.
+<br />
+<br />
+The
+client
+has
+retrieved
+the
+whole
+collection,
+containing
+12
+TDs.
+</aside>
+<p>
+<span class="rfc2119-assertion" id= "tdd-things-list-pagination-collection">
+As
+an
+alternative
+to
+an
+array
+of
+TDs
+as
+the
+body
+of
+the
+response,
+the
+server
+<em class= "rfc2119">
+MAY
+</em>
+send
+a
+more
+verbose
+payload
+allowing
+server-side
+information,
+such
+as
+pagination
+information,
+to
+be
+included
+in
+addition
+to
+the
+actual
+data.
+</span>
+</p>
+<p>
+The
+alternative
+pagination
+format
+is
+inspired
+by
+<a href= "https://www.hydra-cg.com/spec/latest/core/#advanced-concepts">
+Hydra
+Advanced
+Concepts
+</a>,
+more
+concretely
+the
+<a href= "https://www.hydra-cg.com/spec/latest/core/#example-20-a-hydra-partialcollectionview-splits-a-collection-into-multiple-views">
+Partial
+Collection
+View
+</a>.
+Adapted
+to
+our
+purposes
+and
+using
+the
+<i>
+members
+</i>
+field
+to
+accomodate
+the
+array
+of
+TDs,
+it
+looks
+as
+follows
+for
+the
+listing
+endpoint:
+</p>
+<aside class="example" id="example-alternative-payload">
+<div class="marker">
+<a class="self-link" href= "#example-alternative-payload">
+Example
+<bdi>
+9
+</bdi>
+</a>
+<span class= "example-title">:
+Alternative
+payload
+format
+including
+pagination
+information
+</span>
+</div>
+<pre aria-busy="false"><code class="hljs javascript">{
+        <span class="hljs-string">"@context"</span>: <span class=
+"hljs-string">"https://www.w3.org/2022/wot/discovery"</span>,
+        <span class="hljs-string">"@type"</span>: <span class=
+"hljs-string">"ThingCollection"</span>,
+        <span class="hljs-string">"total"</span>: <span class=
+"hljs-number">12</span>,
+        <span class="hljs-string">"members"</span>: [
+                { TD },
+                <span class="hljs-number">9</span> other TDs...
+        ],
+        <span class="hljs-string">"@id"</span>: <span class=
+"hljs-string">"/things?offset=0&amp;limit=10&amp;format=collection"</span>,
+        <span class="hljs-string">"next"</span>: <span class=
+"hljs-string">"/things?offset=10&amp;limit=10&amp;format=collection"</span>
+}
+</code>
+</pre>
+</aside>
+<p>
+To
+tell
+the
+server
+which
+format
+to
+send,
+the
+additional
+query
+parameter
+<code>
+?format=array|collection
+</code>
+can
+be
+added
+to
+the
+request.
+<code>
+?format=array
+</code>
+is
+the
+default
+parameter,
+does
+not
+have
+to
+be
+provided
+explicitly,
+and
+yields
+to
+a
+server
+response
+of
+the
+pure
+array
+of
+TDs.
+<code>
+?format=collection
+</code>
+should
+yield
+to
+a
+server
+response
+with
+the
+format
+as
+described
+in
+<a href= "#example-alternative-payload" data-matched-text= "[[[#example-alternative-payload]]]" class="box-ref">
+Example
+<bdi>
+9
+</bdi>
+</a>.
+</p>
+<p>
+The
+listing
+operation
+is
+specified
+as
+<code>
+things
+</code>
+property
+in
+<a href="#directory-api-spec" data-matched-text= "[[[#directory-api-spec]]]" class="sec-ref">
+<bdi class= "secno">
+7.3.2.4
+</bdi>
+API
+Specification
+(Thing
+Model)
+</a>.
+</p>
+</section>
+<section id="exploration-directory-api-things-validation" class= "normative">
+<div class="header-wrapper">
+<h6 id="x7-3-2-1-6-validation">
+<bdi class="secno">
+7.3.2.1.6
+</bdi>
+Validation
+</h6>
+<a class="self-link" href= "#exploration-directory-api-things-validation" aria-label= "Permalink for Section 7.3.2.1.6">
+</a>
+</div>
+<p>
+<span class="rfc2119-assertion" id= "tdd-validation-syntactic">
+The
+syntactic
+validation
+of
+TD
+objects
+before
+storage
+is
+<em class="rfc2119">
+RECOMMENDED
+</em>
+to
+prevent
+common
+erroneous
+submissions.
+</span>
+<span class= "rfc2119-assertion" id="tdd-validation-jsonschema">
+The
+server
+<em class="rfc2119">
+SHOULD
+</em>
+use
+at
+least
+<a href= "https://www.w3.org/TR/wot-thing-description11/#minimal-validation-serialization-json">
+Minimal
+Validation
+</a>
+as
+defined
+in
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href="#bib-wot-thing-description11" title= "Web of Things (WoT) Thing Description 1.1">
+wot-thing-description11
+</a>
+</cite>
+]
+to
+validate
+TDs,
+including
+use
+of
+the
+<a href= "https://www.w3.org/TR/wot-thing-description/#json-schema-for-validation">
+WoT
+Thing
+Description
+(1.0)
+JSON
+Schema
+</a>
+or
+<a href= "https://www.w3.org/TR/wot-thing-description11/#json-schema-for-validation">
+WoT
+Thing
+Description
+1.1
+JSON
+Schema
+</a>,
+and
+the
+JSON
+schema
+defined
+in
+<a href="#tdd-extensions-jsonschema" data-matched-text= "[[[#tdd-extensions-jsonschema]]]" class="sec-ref">
+<bdi class= "secno">
+A.
+</bdi>
+JSON
+Schema
+for
+WoT
+Discovery
+TD-extensions
+</a>
+for
+<a href="#dfn-wot-enriched-thing-description" class= "internalDFN" data-link-type="dfn" id= "ref-for-dfn-wot-enriched-thing-description-6">
+Enriched
+TDs
+</a>,
+as
+appropriate
+based
+on
+the
+value
+of
+the
+<code>
+@context
+</code>.
+</span>
+</p>
+<p>
+Additional
+forms
+of
+validation
+can
+be
+added
+to
+support
+various
+use
+cases.
+For
+example,
+a
+use
+case
+may
+require
+stateful
+validation
+of
+the
+input
+TDs
+to
+ensure
+that
+the
+<code>
+version
+</code>
+value
+is
+initialized
+and
+updated
+according
+to
+pre-defined
+rules.
+</p>
+<p>
+<span class="rfc2119-assertion" id="tdd-validation-result">
+If
+the
+server
+fails
+to
+validate
+the
+TD
+object,
+it
+<em class= "rfc2119">
+MUST
+</em>
+inform
+the
+client
+with
+necessary
+details
+to
+identify
+and
+resolve
+the
+errors.
+</span>
+<span class= "rfc2119-assertion" id="tdd-validation-response">
+The
+validation
+error
+<em class="rfc2119">
+MUST
+</em>
+be
+described
+as
+Problem
+Details
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href= "#bib-rfc7807" title= "Problem Details for HTTP APIs">
+RFC7807
+</a>
+</cite>
+]
+with
+an
+extension
+field
+called
+<code>
+validationErrors
+</code>,
+set
+to
+an
+array
+of
+objects
+with
+<code>
+field
+</code>
+and
+<code>
+description
+</code>
+fields.
+</span>
+This
+is
+necessary
+to
+represent
+the
+error
+in
+a
+machine-readable
+way.
+<span class= "rfc2119-assertion" id="tdd-validation-response-utf-8">
+All
+validation
+error
+responses
+described
+using
+Problem
+Details
+<em class="rfc2119">
+MUST
+</em>
+be
+encoded
+using
+UTF-8.
+</span>
+As
+already
+stated
+in
+general
+for
+error
+reporting,
+validation
+error
+responses
+may
+report
+details
+in
+different
+languages
+using
+proactive
+negotiation,
+if
+the
+<code>
+Accept-Language
+</code>
+header
+field
+has
+been
+set
+in
+the
+HTTP
+request
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href="#bib-rfc7231" title= "Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content">
+RFC7231
+</a>
+</cite>
+].
+</p>
+<p>
+<a href="#example-validation-error" data-matched-text= "[[[#example-validation-error]]]" class="box-ref">
+Example
+<bdi>
+10
+</bdi>
+</a>
+is
+an
+example
+error
+response
+with
+two
+validation
+errors.
+</p>
+<aside class="example" id="example-validation-error">
+<div class="marker">
+<a class="self-link" href= "#example-validation-error">
+Example
+<bdi>
+10
+</bdi>
+</a>
+<span class= "example-title">:
+Example
+validation
+error
+response
+</span>
+</div>
+<pre aria-busy="false"><code class="hljs json">{
+    <span class="hljs-attr">"title"</span>: <span class=
+"hljs-string">"Bad Request"</span>,
+    <span class="hljs-attr">"status"</span>: <span class=
+"hljs-number">400</span>,
+    <span class="hljs-attr">"detail"</span>: <span class=
+"hljs-string">"The input did not pass the JSON Schema validation"</span>,
+    <span class="hljs-attr">"instance"</span>: <span class=
+"hljs-string">"/errors/30585584-cce2-4d04-8079-67b33ffdafbc"</span>,
+    <span class="hljs-attr">"validationErrors"</span>: [
+        {
+            <span class="hljs-attr">"field"</span>: <span class=
+"hljs-string">"(root)"</span>,
+            <span class=
+"hljs-attr">"description"</span>: <span class=
+"hljs-string">"security is required"</span>
+        },
+        {
+            <span class="hljs-attr">"field"</span>: <span class=
+"hljs-string">"properties.status.forms.0.href"</span>,
+            <span class=
+"hljs-attr">"description"</span>: <span class=
+"hljs-string">"Invalid type. Expected: string, given: integer"</span>
+        }
+    ]
+}
+</code>
+</pre>
+</aside>
+</section>
+</section>
+<section id="exploration-directory-api-notification" class= "normative">
+<div class="header-wrapper">
+<h5 id="x7-3-2-2-events-api">
+<bdi class="secno">
+7.3.2.2
+</bdi>
+Events
+API
+</h5>
+<a class="self-link" href="#exploration-directory-api-notification" aria-label="Permalink for Section 7.3.2.2">
+</a>
+</div>
+<p>
+The
+Notification
+API
+is
+to
+notify
+clients
+about
+the
+changes
+to
+<a href="#dfn-td" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-td-43">
+TDs
+</a>
+maintained
+within
+the
+directory.
+<span class="rfc2119-assertion" id="tdd-notification">
+Directories
+<em class="rfc2119">
+MAY
+</em>
+implement
+the
+Notification
+API.
+</span>
+</p>
+<p>
+<span class="rfc2119-assertion" id="tdd-notification-sse">
+The
+Notification
+API
+<em class="rfc2119">
+MUST
+</em>
+follow
+the
+Server-Sent
+Events
+(SSE)
+[
+<cite>
+<a class="bibref" data-link-type= "biblio" href="#bib-html" title="HTML Standard">
+HTML
+</a>
+</cite>
+]
+specifications
+to
+serve
+events
+to
+clients
+at
+<code>
+/events
+</code>
+endpoint.
+</span>
+In
+particular,
+the
+server
+responds
+to
+successful
+requests
+with
+200
+(OK)
+status
+and
+<code>
+text/event-stream
+</code>
+Content
+Type.
+Re-connecting
+clients
+may
+continue
+from
+the
+last
+event
+by
+providing
+the
+last
+event
+ID
+as
+<code>
+Last-Event-ID
+</code>
+header
+value.
+<span class="rfc2119-assertion" id= "tdd-notification-event-id">
+The
+server
+<em class= "rfc2119">
+SHOULD
+</em>
+provide
+an
+event
+ID
+as
+the
+<code>
+id
+</code>
+field
+in
+each
+event
+and
+respond
+to
+re-connecting
+clients
+by
+delivering
+all
+missed
+events.
+</span>
+</p>
+<p>
+The
+rest
+of
+this
+section
+describes
+the
+implementation
+details
+on
+top
+of
+the
+SSE
+protocol.
+Realizing
+the
+notification
+functionality
+using
+other
+protocols
+such
+as
+MQTT
+are
+possible
+and
+may
+be
+formalized
+in
+future
+versions
+of
+this
+specification.
+</p>
+<dl>
+<dt>
+Event
+Types
+</dt>
+<dd>
+<span class="rfc2119-assertion" id= "tdd-notification-event-types">
+The
+server
+<em class= "rfc2119">
+MUST
+</em>
+produce
+events
+attributed
+to
+the
+lifecycle
+of
+the
+Thing
+Descriptions
+within
+the
+directory
+using
+<code>
+thing_created
+</code>,
+<code>
+thing_updated
+</code>,
+and
+<code>
+thing_deleted
+</code>
+event
+types.
+</span>
+</dd>
+<dt>
+Event
+Filtering
+</dt>
+<dd>
+The
+API
+enables
+server-side
+filtering
+of
+events
+to
+reduce
+resource
+consumption
+by
+delivering
+only
+the
+events
+required
+by
+clients.
+Client
+libraries
+may
+offer
+additional
+filtering
+capabilities
+on
+the
+client-side.
+<p>
+<span class="rfc2119-assertion" id= "tdd-notification-filter-type">
+The
+server
+<em class= "rfc2119">
+MUST
+</em>
+support
+event
+filtering
+based
+on
+the
+event
+type
+given
+by
+the
+client
+upon
+subscription.
+</span>
+</p>
+<p>
+For
+example,
+given
+the
+URI
+Template
+<code>
+/events{/type}
+</code>:
+</p>
+<ul>
+<li>
+<code>
+/events/thing_created
+</code>
+instructs
+the
+server
+to
+only
+deliver
+events
+of
+type
+<code>
+thing_created
+</code>
+</li>
+<li>
+<code>
+/events
+</code>
+instructs
+the
+server
+to
+deliver
+all
+events
+</li>
+</ul>
+<p>
+The
+clients
+need
+to
+subscribe
+separately
+to
+receive
+a
+subset
+of
+the
+events
+(e.g.
+only
+<code>
+thing_created
+</code>
+and
+<code>
+thing_deleted
+</code>
+)
+from
+the
+server.
+When
+using
+HTTP/2,
+multiple
+subscriptions
+on
+the
+same
+domain
+(HTTP
+streams)
+get
+multiplexed
+on
+a
+single
+connection.
+</p>
+</dd>
+<dt>
+Event
+Data
+</dt>
+<dd>
+<p>
+<span class="rfc2119-assertion" id="tdd-notification-data">
+The
+event
+data
+<em class="rfc2119">
+MUST
+</em>
+contain
+the
+JSON
+serialization
+of
+the
+event
+object.
+</span>
+The
+event
+data
+object
+is
+a
+<a href="#dfn-wot-partial-thing-description" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-wot-partial-thing-description-2">
+Partial
+TD
+</a>
+or
+the
+whole
+<a href="#dfn-td" class="internalDFN" data-link-type="dfn" id="ref-for-dfn-td-44">
+TD
+</a>
+object
+depending
+on
+the
+request:
+</p>
+<ul>
+<li>
+<span class="rfc2119-assertion" id= "tdd-notification-data-td-id">
+The
+event
+data
+object
+<em class= "rfc2119">
+MUST
+</em>
+at
+least
+include
+the
+identifier
+of
+the
+TD
+created,
+updated,
+or
+deleted
+at
+that
+event
+in
+<a href= "#dfn-wot-partial-thing-description" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-wot-partial-thing-description-3">
+Partial
+TD
+</a>
+form.
+</span>
+<aside class="example" id= "example-creation-and-deletion-sse-events-for-a-td">
+<div class="marker">
+<a class="self-link" href= "#example-creation-and-deletion-sse-events-for-a-td">
+Example
+<bdi>
+11
+</bdi>
+</a>
+<span class="example-title">:
+Creation
+and
+deletion
+SSE
+events
+for
+a
+TD
+</span>
+</div>
+<pre aria-busy="false"><code class="hljs css">event: thing_created
+data: {<span class="hljs-string">"id"</span>: <span class=
+"hljs-string">"urn:example:simple-td"</span>}
+id: event_1
+event: thing_deleted
+data: {<span class="hljs-string">"id"</span>: <span class=
+"hljs-string">"urn:example:simple-td"</span>}
+id:
+event_2
+</code>
+</pre>
+</aside>
+</li>
+<li>
+<span class="rfc2119-assertion" id= "tdd-notification-data-create-full">
+When
+<code>
+diff
+</code>
+query
+parameter
+is
+set
+to
+<code>
+true
+</code>
+and
+the
+event
+has
+<code>
+thing_created
+</code>
+type,
+the
+server
+<em class= "rfc2119">
+MAY
+</em>
+return
+the
+whole
+TD
+object
+as
+event
+data.
+</span>
+<aside class="example" id="example-create-event-full">
+<div class="marker">
+<a class="self-link" href= "#example-create-event-full">
+Example
+<bdi>
+12
+</bdi>
+</a>
+<span class= "example-title">:
+Full
+creation
+SSE
+event
+for
+a
+TD
+</span>
+</div>
+<pre aria-busy="false"><code class="hljs css">event: thing_created
+data: {
+data:     <span class="hljs-string">"@context"</span>: [
+data:         <span class=
+"hljs-string">"https://www.w3.org/2022/wot/td/v1.1"</span>,
+data:         <span class=
+"hljs-string">"https://www.w3.org/2022/wot/discovery"</span>
+data:     ],
+data:     <span class=
+"hljs-string">"description"</span>: <span class=
+"hljs-string">"This is a new TD"</span>,
+data:     <span class="hljs-string">"id"</span>: <span class=
+"hljs-string">"urn:example:simple-td"</span>,
+data:     <span class="hljs-string">"security"</span>: <span class=
+"hljs-string">"basic_sc"</span>,
+data:     <span class="hljs-string">"securityDefinitions"</span>: {
+data:         <span class="hljs-string">"basic_sc"</span>: {
+data:             <span class=
+"hljs-string">"scheme"</span>: <span class=
+"hljs-string">"basic"</span>
+data:         }
+data:     },
+data:     <span class="hljs-string">"registration"</span>: {
+data:         <span class=
+"hljs-string">"created"</span>: <span class=
+"hljs-string">"2021-01-19T17:02:00Z"</span>,
+data:         <span class=
+"hljs-string">"modified"</span>: <span class=
+"hljs-string">"2021-01-19T17:02:00Z"</span>
+data:     },
+data:     <span class="hljs-string">"title"</span>: <span class=
+"hljs-string">"Simple TD"</span>
+data: }
+id:
+event_1
+</code>
+</pre>
+</aside>
+</li>
+<li>
+<span class="rfc2119-assertion" id= "tdd-notification-data-update-diff">
+When
+<code>
+diff
+</code>
+query
+parameter
+is
+set
+to
+<code>
+true
+</code>
+and
+the
+event
+has
+<code>
+thing_updated
+</code>
+type,
+the
+server
+<em class= "rfc2119">
+MAY
+</em>
+inform
+the
+client
+about
+the
+updated
+parts
+following
+the
+JSON
+Merge
+Patch
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href="#bib-rfc7396" title= "JSON Merge Patch">
+RFC7396
+</a>
+</cite>
+]
+format.
+</span>
+<span class= "rfc2119-assertion" id="tdd-notification-data-update-id">
+A
+<code>
+thing_updated
+</code>
+event
+data
+that
+is
+based
+on
+JSON
+Merge
+Patch
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href= "#bib-rfc7396" title="JSON Merge Patch">
+RFC7396
+</a>
+</cite>
+]
+<em class="rfc2119">
+MUST
+</em>
+always
+include
+the
+identifier
+of
+the
+TD
+regardless
+of
+whether
+it
+is
+changed.
+</span>
+<p>
+The
+following
+example
+shows
+the
+event
+triggered
+on
+update
+of
+the
+TD
+from
+<a href="#example-create-event-full" data-matched-text= "[[[#example-create-event-full]]]" class="box-ref">
+Example
+<bdi>
+12
+</bdi>
+</a>:
+</p>
+<aside class="example" id="example-update-event-full">
+<div class="marker">
+<a class="self-link" href= "#example-update-event-full">
+Example
+<bdi>
+13
+</bdi>
+</a>
+<span class= "example-title">:
+Full
+update
+SSE
+event
+for
+a
+TD
+with
+removed
+description
+and
+changed
+title
+</span>
+</div>
+<pre aria-busy="false"><code class="hljs css">event: thing_updated
+data: {
+data:     <span class="hljs-string">"description"</span>: null,
+data:     <span class="hljs-string">"id"</span>: <span class=
+"hljs-string">"urn:example:simple-td"</span>,
+data:     <span class="hljs-string">"title"</span>: <span class=
+"hljs-string">"Updated TD"</span>
+data: }
+id:
+event_3
+</code>
+</pre>
+</aside>
+</li>
+<li>
+<span class="rfc2119-assertion" id= "tdd-notification-data-delete-diff">
+The
+<code>
+diff
+</code>
+query
+parameter
+<em class="rfc2119">
+MUST
+</em>
+be
+ignored
+for
+<code>
+thing_deleted
+</code>
+events.
+</span>
+In
+other
+words,
+the
+server
+shall
+not
+include
+additional
+properties
+in
+the
+payload
+of
+<code>
+thing_deleted
+</code>
+events
+when
+<code>
+diff
+</code>
+is
+set
+to
+<code>
+true
+</code>.
+</li>
+<li>
+When
+a
+server
+which
+does
+not
+support
+the
+<code>
+diff
+</code>
+query
+parameter
+is
+requested
+with
+such
+query
+parameter,
+it
+should
+reject
+the
+request.
+This
+is
+to
+inform
+clients
+about
+the
+lack
+of
+such
+functionality
+at
+connection
+time
+and
+avoid
+runtime
+exceptions
+caused
+by
+missing
+event
+data
+attributes.
+</li>
+</ul>
+</dd>
+</dl>
+<p>
+The
+Notification
+API
+is
+specified
+as
+three
+event
+affordances
+in
+<a href="#directory-api-spec" data-matched-text= "[[[#directory-api-spec]]]" class="sec-ref">
+<bdi class= "secno">
+7.3.2.4
+</bdi>
+API
+Specification
+(Thing
+Model)
+</a>,
+namely:
+<code>
+thingCreated
+</code>,
+<code>
+thingUpdated
+</code>,
+and
+<code>
+thingDeleted
+</code>.
+</p>
+<div class="note" role="note" id="issue-container-generatedID-0">
+<div role="heading" class="note-title marker" id="h-note" aria-level="6">
+<span>
+Note
+</span>
+<span class="issue-label">:
+SSE
+Authorization
+Header
+</span>
+</div>
+<p class="">
+Some
+early
+SSE
+implementations
+(including
+HTML5
+EventSource)
+do
+not
+allow
+setting
+custom
+headers
+in
+the
+initial
+HTTP
+request.
+Authorization
+header
+is
+required
+in
+few
+OAuth2
+flows
+and
+passing
+it
+as
+a
+query
+parameter
+is
+<a href= "https://datatracker.ietf.org/doc/html/rfc6750#section-2.3">
+not
+advised
+</a>.
+There
+are
+polyfills
+for
+browsers
+and
+modern
+libraries
+which
+allow
+setting
+Authorization
+header.
+</p>
+</div>
+</section>
+<section id="exploration-directory-api-search" class="normative">
+<div class="header-wrapper">
+<h5 id="x7-3-2-3-search-api">
+<bdi class="secno">
+7.3.2.3
+</bdi>
+Search
+API
+</h5>
+<a class="self-link" href="#exploration-directory-api-search" aria-label="Permalink for Section 7.3.2.3">
+</a>
+</div>
+<div class="note" id="issue-container-generatedID-1">
+<div role="heading" class="ednote-title marker" id="h-ednote-0" aria-level="6">
+<span>
+Editor's
+note
+</span>
+<span class= "issue-label">:
+Search
+API
+Overview
+</span>
+</div>
+<p class="">
+Sub-API
+to
+search
+a
+directory,
+e.g.
+issue
+a
+query.
+There
+are
+different
+forms
+and
+levels
+of
+query
+possible,
+for
+example,
+syntactic
+(JSONPath,
+XPath)
+vs.
+semantic
+(SPARQL),
+and
+the
+more
+advanced
+query
+types
+may
+not
+be
+supported
+by
+all
+directories.
+So
+this
+API
+will
+have
+further
+subsections,
+some
+of
+which
+will
+be
+optional.
+Search
+also
+includes
+a
+sub-API
+for
+managing
+listing
+the
+contents
+(e.g.
+returned
+by
+a
+query)
+including
+handling
+pagination,
+etc.
+Note
+that
+one
+special
+form
+of
+query
+will
+be
+able
+to
+return
+everything.
+Results
+may
+be
+subject
+to
+the
+requestor's
+authorization.
+<br />
+To
+discuss
+further:
+Federated
+queries
+to
+other
+TDDs,
+Spatial
+and
+network-limited
+queries,
+Links
+</p>
+</div>
+This
+specification
+describes
+three
+search
+APIs:
+syntactic
+search
+with
+JSONPath
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href="#bib-jsonpath" title= "JSONPath: Query expressions for JSON">
+JSONPATH
+</a>
+</cite>
+],
+syntactic
+search
+with
+XPath
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href="#bib-xpath-31" title= "XML Path Language (XPath) 3.1">
+xpath-31
+</a>
+</cite>
+],
+and
+semantic
+search
+with
+SPARQL
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href="#bib-sparql11-overview" title= "SPARQL 1.1 Overview">
+sparql11-overview
+</a>
+</cite>
+].
+<span class= "rfc2119-assertion" id="tdd-search-sparql">
+The
+Directory
+<em class= "rfc2119">
+MAY
+</em>
+implement
+semantic
+search
+with
+SPARQL.
+</span>
+JSONPath
+and
+XPath
+are
+informative
+and
+subject
+to
+change.
+<p>
+<span class="rfc2119-assertion" id="tdd-search-large-tdds">
+It
+is
+<em class="rfc2119">
+RECOMMENDED
+</em>
+that
+directories
+implement
+a
+search
+API
+to
+efficiently
+serve
+<a href="#dfn-td" class= "internalDFN" data-link-type="dfn" id="ref-for-dfn-td-45">
+TDs
+</a>
+based
+on
+client-specific
+queries.
+</span>
+</p>
+<section id="jsonpath-semantic" class="informative">
+<div class="header-wrapper">
+<h6 id="x7-3-2-3-1-syntactic-search-jsonpath">
+<bdi class= "secno">
+7.3.2.3.1
+</bdi>
+Syntactic
+search:
+JSONPath
+</h6>
+<a class="self-link" href="#jsonpath-semantic" aria-label= "Permalink for Section 7.3.2.3.1">
+</a>
+</div>
+<p>
+<em>
+This
+section
+is
+non-normative.
+</em>
+</p>
+Support
+for
+JSONPath
+Search
+API
+is
+optional.
+If
+implemented,
+the
+JSONPath
+API
+must
+allow
+searching
+TDs
+using
+an
+HTTP
+<code>
+GET
+</code>
+request
+at
+<code>
+/search/jsonpath?query={query}
+</code>
+endpoint,
+where
+<code>
+query
+</code>
+is
+the
+JSONPath
+expression.
+The
+request
+must
+contain
+a
+valid
+JSONPath
+[
+<cite>
+<a class="bibref" data-link-type= "biblio" href="#bib-jsonpath" title= "JSONPath: Query expressions for JSON">
+JSONPATH
+</a>
+</cite>
+]
+as
+searching
+parameter.
+A
+successful
+response
+must
+have
+200
+(OK)
+status,
+contain
+<code>
+application/json
+</code>
+in
+the
+Content-Type
+header,
+and
+a
+set
+of
+complete
+TDs
+or
+a
+set
+of
+TD
+fragments
+in
+the
+body.
+The
+syntactic
+search
+with
+JSONPath
+is
+specified
+as
+<code>
+searchJSONPath
+</code>
+action
+in
+<a href="#directory-api-spec" data-matched-text="[[[#directory-api-spec]]]" class= "sec-ref">
+<bdi class="secno">
+7.3.2.4
+</bdi>
+API
+Specification
+(Thing
+Model)
+</a>.
+</section>
+<section id="xpath-semantic" class="informative">
+<div class="header-wrapper">
+<h6 id="x7-3-2-3-2-syntactic-search-xpath">
+<bdi class= "secno">
+7.3.2.3.2
+</bdi>
+Syntactic
+search:
+XPath
+</h6>
+<a class="self-link" href="#xpath-semantic" aria-label= "Permalink for Section 7.3.2.3.2">
+</a>
+</div>
+<p>
+<em>
+This
+section
+is
+non-normative.
+</em>
+</p>
+Support
+for
+XPath
+Search
+API
+is
+optional.
+If
+implemented,
+the
+XPath
+query
+API
+must
+allow
+searching
+TDs
+using
+an
+HTTP
+<code>
+GET
+</code>
+request
+at
+<code>
+/search/xpath?query={query}
+</code>
+endpoint,
+where
+<code>
+query
+</code>
+is
+the
+XPath
+expression.
+The
+request
+must
+contain
+a
+valid
+XPath
+3.1
+[
+<cite>
+<a class="bibref" data-link-type= "biblio" href="#bib-xpath-31" title= "XML Path Language (XPath) 3.1">
+xpath-31
+</a>
+</cite>
+]
+as
+search
+parameter.
+A
+successful
+response
+must
+have
+200
+(OK)
+status,
+contain
+<code>
+application/json
+</code>
+in
+the
+Content-Type
+header,
+and
+the
+query
+response
+in
+JSON
+serialization
+in
+the
+body.
+The
+data
+schema
+for
+the
+response
+is
+defined
+implicitly
+by
+the
+query
+and
+the
+XPath
+specification.
+The
+syntactic
+search
+with
+XPath
+is
+specified
+as
+<code>
+searchXPath
+</code>
+action
+in
+<a href="#directory-api-spec" data-matched-text="[[[#directory-api-spec]]]" class= "sec-ref">
+<bdi class="secno">
+7.3.2.4
+</bdi>
+API
+Specification
+(Thing
+Model)
+</a>.
+</section>
+<section id="search-semantic" class="normative">
+<div class="header-wrapper">
+<h6 id="x7-3-2-3-3-semantic-search-sparql">
+<bdi class= "secno">
+7.3.2.3.3
+</bdi>
+Semantic
+search:
+SPARQL
+</h6>
+<a class="self-link" href="#search-semantic" aria-label= "Permalink for Section 7.3.2.3.3">
+</a>
+</div>
+Support
+for
+SPARQL
+Search
+API
+is
+optional.
+<span class= "rfc2119-assertion" id="tdd-search-sparql-version">
+If
+implemented,
+the
+SPARQL
+search
+API
+<em class="rfc2119">
+MUST
+</em>
+allow
+searching
+TDs
+using
+the
+SPARQL
+1.1
+protocol
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href="#bib-sparql11-overview" title= "SPARQL 1.1 Overview">
+sparql11-overview
+</a>
+</cite>
+].
+</span>
+<span class="rfc2119-assertion" id= "tdd-search-sparql-method-get">
+The
+SPARQL
+API
+<em class= "rfc2119">
+MUST
+</em>
+accept
+queries
+using
+HTTP
+<code>
+GET
+</code>
+requests
+at
+<code>
+/search/sparql?query={query}
+</code>
+endpoint,
+where
+<code>
+query
+</code>
+is
+the
+SPARQL
+expression.
+</span>
+<span class="rfc2119-assertion" id= "tdd-search-sparql-method-post">
+The
+support
+for
+SPARQL
+search
+using
+HTTP
+<code>
+POST
+</code>
+method
+at
+<code>
+/search/sparql
+</code>
+endpoint
+is
+<em class="rfc2119">
+OPTIONAL
+</em>.
+</span>
+<span class= "rfc2119-assertion" id="tdd-search-sparql-resp-select-ask">
+A
+successful
+request
+with
+a
+query
+<code>
+SELECT
+</code>
+or
+<code>
+ASK
+</code>
+<em class="rfc2119">
+MUST
+</em>
+return
+a
+response
+200
+(OK)
+status,
+and
+contain
+<code>
+application/json
+</code>
+by
+default
+in
+the
+Content-Type
+header.
+</span>
+<span class= "rfc2119-assertion" id= "tdd-search-sparql-resp-describe-construct">
+A
+successful
+request
+with
+a
+query
+<code>
+CONSTRUCT
+</code>
+and
+<code>
+DESCRIBE
+</code>
+<em class="rfc2119">
+MUST
+</em>
+return
+a
+response
+200
+(OK)
+status,
+and
+contain
+<code>
+application/ld+json
+</code>
+by
+default
+in
+the
+Content-Type
+header.
+</span>
+<span class="rfc2119-assertion" id= "tdd-search-sparql-error">
+A
+request
+with
+any
+query
+different
+from
+<code>
+SELECT
+</code>,
+<code>
+ASK
+</code>,
+<code>
+CONSTRUCT
+</code>
+or
+<code>
+DESCRIBE
+</code>
+<em class="rfc2119">
+MUST
+</em>
+return
+a
+response
+400
+(Bad
+Request).
+</span>
+The
+semantic
+search
+with
+SPARQL
+is
+specified
+as
+<code>
+searchSPARQL
+</code>
+action
+in
+<a href= "#directory-api-spec" data-matched-text="[[[#directory-api-spec]]]" class="sec-ref">
+<bdi class="secno">
+7.3.2.4
+</bdi>
+API
+Specification
+(Thing
+Model)
+</a>.
+<span class="rfc2119-assertion" id= "tdd-search-sparql-federation">
+A
+WoT
+Thing
+Description
+Directory
+<em class="rfc2119">
+MAY
+</em>
+implement
+federation
+in
+its
+SPARQL
+query
+API.
+</span>
+<span class="rfc2119-assertion" id= "tdd-search-sparql-federation-version">
+If
+implemented,
+the
+SPARQL
+API
+<em class="rfc2119">
+MUST
+</em>
+implement
+the
+SPARQL
+1.1
+Federated
+Query
+standard
+[
+<cite>
+<a class="bibref" data-link-type= "biblio" href="#bib-sparql11-overview" title= "SPARQL 1.1 Overview">
+sparql11-overview
+</a>
+</cite>
+].
+</span>
+</section>
+</section>
+<section id="directory-api-spec">
+<div class="header-wrapper">
+<h5 id="x7-3-2-4-api-specification-thing-model">
+<bdi class= "secno">
+7.3.2.4
+</bdi>
+API
+Specification
+(Thing
+Model)
+</h5>
+<a class="self-link" href="#directory-api-spec" aria-label= "Permalink for Section 7.3.2.4">
+</a>
+</div>
+<p>
+A
+template
+for
+the
+API
+of
+Thing
+Description
+Directories
+is
+given
+here
+as
+a
+<a href="#dfn-thing-model" class="internalDFN" data-link-type="dfn" id="ref-for-dfn-thing-model-1">
+Thing
+Model
+</a>.
+The
+Thing
+Model
+is
+normative
+(except
+where
+noted)
+but
+should
+not
+be
+considered
+as
+the
+sole
+reference
+to
+implement
+or
+interact
+with
+a
+Thing
+Description
+Directory.
+Please
+refer
+also
+to
+the
+specifications
+given
+in
+<a href="#exploration-directory-api" data-matched-text="[[[#exploration-directory-api]]]" class= "sec-ref">
+<bdi class="secno">
+7.3.2
+</bdi>
+Directory
+Service
+API
+</a>.
+</p>
+<p>
+The
+<code>
+searchJSONPath
+</code>
+and
+<code>
+searchXPath
+</code>
+affordances
+given
+in
+this
+Thing
+Model
+are
+not
+normative
+and
+are
+provided
+for
+information
+only.
+</p>
+<p>
+Note
+that
+a
+<code>
+contentType
+</code>
+is
+required
+by
+the
+WoT
+TD
+1.1
+specification
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href="#bib-wot-thing-description11" title= "Web of Things (WoT) Thing Description 1.1">
+wot-thing-description11
+</a>
+</cite>
+]
+for
+instances
+of
+the
+<code>
+ExpectedResponse
+</code>
+class
+(i.e.,
+the
+JSON
+object
+corresponding
+to
+the
+key
+<code>
+response
+</code>
+in
+a
+form),
+even
+when
+the
+body
+of
+the
+HTTP
+response
+is
+supposed
+to
+be
+empty.
+In
+this
+case,
+<code>
+application/x-empty
+</code>
+can
+be
+used
+to
+ensure
+that
+the
+TD
+generated
+from
+the
+TM
+below
+is
+valid.
+</p>
+<pre class="advisement" aria-busy="false"><code class="hljs json">{
+    <span class="hljs-attr">"@context"</span>: [
+        <span class=
+"hljs-string">"https://www.w3.org/2022/wot/td/v1.1"</span>,
+        <span class=
+"hljs-string">"https://www.w3.org/2022/wot/discovery"</span>
+    ],
+    <span class="hljs-attr">"@type"</span>: [
+        <span class="hljs-string">"tm:ThingModel"</span>,
+        <span class="hljs-string">"ThingDirectory"</span>
+    ],
+    <span class="hljs-attr">"title"</span>: <span class=
+"hljs-string">"Thing Description Directory (TDD) Thing Model"</span>,
+    <span class="hljs-attr">"version"</span>: {
+        <span class="hljs-attr">"model"</span>: <span class=
+"hljs-string">"1.0.0"</span>
+    },
+    <span class="hljs-attr">"base"</span>: <span class=
+"hljs-string">"{{DIRECTORY_BASE_URL}}"</span>,
+    <span class="hljs-attr">"tm:optional"</span>: [
+        <span class="hljs-string">"/actions/createThing"</span>,
+        <span class=
+"hljs-string">"/actions/createAnonymousThing"</span>,
+        <span class="hljs-string">"/actions/retrieveThing"</span>,
+        <span class="hljs-string">"/actions/updateThing"</span>,
+        <span class=
+"hljs-string">"/actions/partiallyUpdateThing"</span>,
+        <span class="hljs-string">"/actions/deleteThing"</span>,
+        <span class="hljs-string">"/actions/searchJSONPath"</span>,
+        <span class="hljs-string">"/actions/searchXPath"</span>,
+        <span class="hljs-string">"/actions/searchSPARQL"</span>,
+        <span class="hljs-string">"/events/thingCreated"</span>,
+        <span class="hljs-string">"/events/thingUpdated"</span>,
+        <span class="hljs-string">"/events/thingDeleted"</span>
+    ],
+    <span class="hljs-attr">"properties"</span>: {
+        <span class="hljs-attr">"things"</span>: {
+            <span class=
+"hljs-attr">"description"</span>: <span class=
+"hljs-string">"Retrieve all Thing Descriptions"</span>,
+            <span class="hljs-attr">"uriVariables"</span>: {
+                <span class="hljs-attr">"offset"</span>: {
+                    <span class=
+"hljs-attr">"title"</span>: <span class=
+"hljs-string">"Number of TDs to skip before the page"</span>,
+                    <span class=
+"hljs-attr">"type"</span>: <span class=
+"hljs-string">"number"</span>,
+                    <span class=
+"hljs-attr">"default"</span>: <span class="hljs-number">0</span>
+                },
+                <span class="hljs-attr">"limit"</span>: {
+                    <span class=
+"hljs-attr">"title"</span>: <span class=
+"hljs-string">"Number of TDs in a page"</span>,
+                    <span class=
+"hljs-attr">"type"</span>: <span class=
+"hljs-string">"number"</span>
+                },
+                <span class="hljs-attr">"format"</span>: {
+                    <span class=
+"hljs-attr">"title"</span>: <span class=
+"hljs-string">"Payload format"</span>,
+                    <span class=
+"hljs-attr">"type"</span>: <span class=
+"hljs-string">"string"</span>,
+                    <span class="hljs-attr">"enum"</span>: [
+                        <span class="hljs-string">"array"</span>,
+                        <span class=
+"hljs-string">"collection"</span>
+                    ],
+                    <span class=
+"hljs-attr">"default"</span>: <span class=
+"hljs-string">"array"</span>
+                }
+            },
+            <span class="hljs-attr">"forms"</span>: [
+                {
+                    <span class=
+"hljs-attr">"href"</span>: <span class=
+"hljs-string">"/things{?offset,limit,format}"</span>,
+                    <span class=
+"hljs-attr">"htv:methodName"</span>: <span class=
+"hljs-string">"GET"</span>,
+                    <span class="hljs-attr">"response"</span>: {
+                        <span class=
+"hljs-attr">"description"</span>: <span class=
+"hljs-string">"Success response"</span>,
+                        <span class=
+"hljs-attr">"htv:statusCodeValue"</span>: <span class=
+"hljs-number">200</span>,
+                        <span class=
+"hljs-attr">"contentType"</span>: <span class=
+"hljs-string">"application/ld+json"</span>,
+                        <span class=
+"hljs-attr">"htv:headers"</span>: [
+                            {
+                                <span class=
+"hljs-attr">"htv:fieldName"</span>: <span class=
+"hljs-string">"Link"</span>
+                            }
+                        ]
+                    },
+                    <span class=
+"hljs-attr">"additionalResponses"</span>: [
+                        {
+                            <span class=
+"hljs-attr">"description"</span>: <span class=
+"hljs-string">"Invalid query arguments"</span>,
+                            <span class=
+"hljs-attr">"contentType"</span>: <span class=
+"hljs-string">"application/problem+json"</span>,
+                            <span class=
+"hljs-attr">"htv:statusCodeValue"</span>: <span class=
+"hljs-number">400</span>
+                        }
+                    ]
+                }
+            ]
+        }
+    },
+    <span class="hljs-attr">"actions"</span>: {
+        <span class="hljs-attr">"createThing"</span>: {
+            <span class=
+"hljs-attr">"description"</span>: <span class=
+"hljs-string">"Create a Thing Description"</span>,
+            <span class="hljs-attr">"uriVariables"</span>: {
+                <span class="hljs-attr">"id"</span>: {
+                    <span class=
+"hljs-attr">"@type"</span>: <span class=
+"hljs-string">"ThingID"</span>,
+                    <span class=
+"hljs-attr">"title"</span>: <span class=
+"hljs-string">"Thing Description ID"</span>,
+                    <span class=
+"hljs-attr">"type"</span>: <span class=
+"hljs-string">"string"</span>,
+                    <span class=
+"hljs-attr">"format"</span>: <span class=
+"hljs-string">"iri-reference"</span>
+                }
+            },
+            <span class="hljs-attr">"input"</span>: {
+                <span class=
+"hljs-attr">"description"</span>: <span class=
+"hljs-string">"The schema is implied by the content type"</span>,
+                <span class="hljs-attr">"type"</span>: <span class=
+"hljs-string">"object"</span>
+            },
+            <span class="hljs-attr">"forms"</span>: [
+                {
+                    <span class=
+"hljs-attr">"href"</span>: <span class=
+"hljs-string">"/things/{id}"</span>,
+                    <span class=
+"hljs-attr">"htv:methodName"</span>: <span class=
+"hljs-string">"PUT"</span>,
+                    <span class=
+"hljs-attr">"contentType"</span>: <span class=
+"hljs-string">"application/td+json"</span>,
+                    <span class="hljs-attr">"response"</span>: {
+                        <span class=
+"hljs-attr">"description"</span>: <span class=
+"hljs-string">"Success response"</span>,
+                        <span class=
+"hljs-attr">"htv:statusCodeValue"</span>: <span class=
+"hljs-number">201</span>
+                    },
+                    <span class=
+"hljs-attr">"additionalResponses"</span>: [
+                        {
+                            <span class=
+"hljs-attr">"description"</span>: <span class=
+"hljs-string">"Invalid serialization or TD"</span>,
+                            <span class=
+"hljs-attr">"contentType"</span>: <span class=
+"hljs-string">"application/problem+json"</span>,
+                            <span class=
+"hljs-attr">"htv:statusCodeValue"</span>: <span class=
+"hljs-number">400</span>
+                        }
+                    ]
+                }
+            ]
+        },
+        <span class="hljs-attr">"createAnonymousThing"</span>: {
+            <span class=
+"hljs-attr">"description"</span>: <span class=
+"hljs-string">"Create an anonymous Thing Description"</span>,
+            <span class="hljs-attr">"input"</span>: {
+                <span class=
+"hljs-attr">"description"</span>: <span class=
+"hljs-string">"The schema is implied by the content type"</span>,
+                <span class="hljs-attr">"type"</span>: <span class=
+"hljs-string">"object"</span>
+            },
+            <span class="hljs-attr">"forms"</span>: [
+                {
+                    <span class=
+"hljs-attr">"href"</span>: <span class=
+"hljs-string">"/things"</span>,
+                    <span class=
+"hljs-attr">"htv:methodName"</span>: <span class=
+"hljs-string">"POST"</span>,
+                    <span class=
+"hljs-attr">"contentType"</span>: <span class=
+"hljs-string">"application/td+json"</span>,
+                    <span class="hljs-attr">"response"</span>: {
+                        <span class=
+"hljs-attr">"description"</span>: <span class=
+"hljs-string">"Success response including the system-generated URI"</span>,
+                        <span class=
+"hljs-attr">"htv:headers"</span>: [
+                            {
+                                <span class=
+"hljs-attr">"description"</span>: <span class=
+"hljs-string">"System-generated URI"</span>,
+                                <span class=
+"hljs-attr">"htv:fieldName"</span>: <span class=
+"hljs-string">"Location"</span>
+                            }
+                        ],
+                        <span class=
+"hljs-attr">"htv:statusCodeValue"</span>: <span class=
+"hljs-number">201</span>
+                    },
+                    <span class=
+"hljs-attr">"additionalResponses"</span>: [
+                        {
+                            <span class=
+"hljs-attr">"description"</span>: <span class=
+"hljs-string">"Invalid serialization or TD"</span>,
+                            <span class=
+"hljs-attr">"contentType"</span>: <span class=
+"hljs-string">"application/problem+json"</span>,
+                            <span class=
+"hljs-attr">"htv:statusCodeValue"</span>: <span class=
+"hljs-number">400</span>
+                        }
+                    ]
+                }
+            ]
+        },
+        <span class="hljs-attr">"retrieveThing"</span>: {
+            <span class=
+"hljs-attr">"description"</span>: <span class=
+"hljs-string">"Retrieve a Thing Description"</span>,
+            <span class="hljs-attr">"uriVariables"</span>: {
+                <span class="hljs-attr">"id"</span>: {
+                    <span class=
+"hljs-attr">"@type"</span>: <span class=
+"hljs-string">"ThingID"</span>,
+                    <span class=
+"hljs-attr">"title"</span>: <span class=
+"hljs-string">"Thing Description ID"</span>,
+                    <span class=
+"hljs-attr">"type"</span>: <span class=
+"hljs-string">"string"</span>,
+                    <span class=
+"hljs-attr">"format"</span>: <span class=
+"hljs-string">"iri-reference"</span>
+                }
+            },
+            <span class="hljs-attr">"output"</span>: {
+                <span class=
+"hljs-attr">"description"</span>: <span class=
+"hljs-string">"The schema is implied by the content type"</span>,
+                <span class="hljs-attr">"type"</span>: <span class=
+"hljs-string">"object"</span>
+            },
+            <span class="hljs-attr">"safe"</span>: <span class=
+"hljs-literal">true</span>,
+            <span class=
+"hljs-attr">"idempotent"</span>: <span class=
+"hljs-literal">true</span>,
+            <span class="hljs-attr">"forms"</span>: [
+                {
+                    <span class=
+"hljs-attr">"href"</span>: <span class=
+"hljs-string">"/things/{id}"</span>,
+                    <span class=
+"hljs-attr">"htv:methodName"</span>: <span class=
+"hljs-string">"GET"</span>,
+                    <span class="hljs-attr">"response"</span>: {
+                        <span class=
+"hljs-attr">"description"</span>: <span class=
+"hljs-string">"Success response"</span>,
+                        <span class=
+"hljs-attr">"htv:statusCodeValue"</span>: <span class=
+"hljs-number">200</span>,
+                        <span class=
+"hljs-attr">"contentType"</span>: <span class=
+"hljs-string">"application/td+json"</span>
+                    },
+                    <span class=
+"hljs-attr">"additionalResponses"</span>: [
+                        {
+                            <span class=
+"hljs-attr">"description"</span>: <span class=
+"hljs-string">"TD with the given id not found"</span>,
+                            <span class=
+"hljs-attr">"contentType"</span>: <span class=
+"hljs-string">"application/problem+json"</span>,
+                            <span class=
+"hljs-attr">"htv:statusCodeValue"</span>: <span class=
+"hljs-number">404</span>
+                        }
+                    ]
+                }
+            ]
+        },
+        <span class="hljs-attr">"updateThing"</span>: {
+            <span class=
+"hljs-attr">"description"</span>: <span class=
+"hljs-string">"Update a Thing Description"</span>,
+            <span class="hljs-attr">"uriVariables"</span>: {
+                <span class="hljs-attr">"id"</span>: {
+                    <span class=
+"hljs-attr">"@type"</span>: <span class=
+"hljs-string">"ThingID"</span>,
+                    <span class=
+"hljs-attr">"title"</span>: <span class=
+"hljs-string">"Thing Description ID"</span>,
+                    <span class=
+"hljs-attr">"type"</span>: <span class=
+"hljs-string">"string"</span>,
+                    <span class=
+"hljs-attr">"format"</span>: <span class=
+"hljs-string">"iri-reference"</span>
+                }
+            },
+            <span class="hljs-attr">"input"</span>: {
+                <span class=
+"hljs-attr">"description"</span>: <span class=
+"hljs-string">"The schema is implied by the content type"</span>,
+                <span class="hljs-attr">"type"</span>: <span class=
+"hljs-string">"object"</span>
+            },
+            <span class="hljs-attr">"forms"</span>: [
+                {
+                    <span class=
+"hljs-attr">"href"</span>: <span class=
+"hljs-string">"/things/{id}"</span>,
+                    <span class=
+"hljs-attr">"htv:methodName"</span>: <span class=
+"hljs-string">"PUT"</span>,
+                    <span class=
+"hljs-attr">"contentType"</span>: <span class=
+"hljs-string">"application/td+json"</span>,
+                    <span class="hljs-attr">"response"</span>: {
+                        <span class=
+"hljs-attr">"description"</span>: <span class=
+"hljs-string">"Success response"</span>,
+                        <span class=
+"hljs-attr">"htv:statusCodeValue"</span>: <span class=
+"hljs-number">204</span>
+                    },
+                    <span class=
+"hljs-attr">"additionalResponses"</span>: [
+                        {
+                            <span class=
+"hljs-attr">"description"</span>: <span class=
+"hljs-string">"Invalid serialization or TD"</span>,
+                            <span class=
+"hljs-attr">"contentType"</span>: <span class=
+"hljs-string">"application/problem+json"</span>,
+                            <span class=
+"hljs-attr">"htv:statusCodeValue"</span>: <span class=
+"hljs-number">400</span>
+                        }
+                    ]
+                }
+            ]
+        },
+        <span class="hljs-attr">"partiallyUpdateThing"</span>: {
+            <span class=
+"hljs-attr">"description"</span>: <span class=
+"hljs-string">"Partially update a Thing Description"</span>,
+            <span class="hljs-attr">"uriVariables"</span>: {
+                <span class="hljs-attr">"id"</span>: {
+                    <span class=
+"hljs-attr">"@type"</span>: <span class=
+"hljs-string">"ThingID"</span>,
+                    <span class=
+"hljs-attr">"title"</span>: <span class=
+"hljs-string">"Thing Description ID"</span>,
+                    <span class=
+"hljs-attr">"type"</span>: <span class=
+"hljs-string">"string"</span>,
+                    <span class=
+"hljs-attr">"format"</span>: <span class=
+"hljs-string">"iri-reference"</span>
+                }
+            },
+            <span class="hljs-attr">"input"</span>: {
+                <span class=
+"hljs-attr">"description"</span>: <span class=
+"hljs-string">"The schema is implied by the content type"</span>,
+                <span class="hljs-attr">"type"</span>: <span class=
+"hljs-string">"object"</span>
+            },
+            <span class="hljs-attr">"forms"</span>: [
+                {
+                    <span class=
+"hljs-attr">"href"</span>: <span class=
+"hljs-string">"/things/{id}"</span>,
+                    <span class=
+"hljs-attr">"htv:methodName"</span>: <span class=
+"hljs-string">"PATCH"</span>,
+                    <span class=
+"hljs-attr">"contentType"</span>: <span class=
+"hljs-string">"application/merge-patch+json"</span>,
+                    <span class="hljs-attr">"response"</span>: {
+                        <span class=
+"hljs-attr">"description"</span>: <span class=
+"hljs-string">"Success response"</span>,
+                        <span class=
+"hljs-attr">"htv:statusCodeValue"</span>: <span class=
+"hljs-number">204</span>
+                    },
+                    <span class=
+"hljs-attr">"additionalResponses"</span>: [
+                        {
+                            <span class=
+"hljs-attr">"description"</span>: <span class=
+"hljs-string">"Invalid serialization or TD"</span>,
+                            <span class=
+"hljs-attr">"contentType"</span>: <span class=
+"hljs-string">"application/problem+json"</span>,
+                            <span class=
+"hljs-attr">"htv:statusCodeValue"</span>: <span class=
+"hljs-number">400</span>
+                        },
+                        {
+                            <span class=
+"hljs-attr">"description"</span>: <span class=
+"hljs-string">"TD with the given id not found"</span>,
+                            <span class=
+"hljs-attr">"contentType"</span>: <span class=
+"hljs-string">"application/problem+json"</span>,
+                            <span class=
+"hljs-attr">"htv:statusCodeValue"</span>: <span class=
+"hljs-number">404</span>
+                        }
+                    ]
+                }
+            ]
+        },
+        <span class="hljs-attr">"deleteThing"</span>: {
+            <span class=
+"hljs-attr">"description"</span>: <span class=
+"hljs-string">"Delete a Thing Description"</span>,
+            <span class="hljs-attr">"uriVariables"</span>: {
+                <span class="hljs-attr">"id"</span>: {
+                    <span class=
+"hljs-attr">"@type"</span>: <span class=
+"hljs-string">"ThingID"</span>,
+                    <span class=
+"hljs-attr">"title"</span>: <span class=
+"hljs-string">"Thing Description ID"</span>,
+                    <span class=
+"hljs-attr">"type"</span>: <span class=
+"hljs-string">"string"</span>,
+                    <span class=
+"hljs-attr">"format"</span>: <span class=
+"hljs-string">"iri-reference"</span>
+                }
+            },
+            <span class="hljs-attr">"forms"</span>: [
+                {
+                    <span class=
+"hljs-attr">"href"</span>: <span class=
+"hljs-string">"/things/{id}"</span>,
+                    <span class=
+"hljs-attr">"htv:methodName"</span>: <span class=
+"hljs-string">"DELETE"</span>,
+                    <span class="hljs-attr">"response"</span>: {
+                        <span class=
+"hljs-attr">"description"</span>: <span class=
+"hljs-string">"Success response"</span>,
+                        <span class=
+"hljs-attr">"htv:statusCodeValue"</span>: <span class=
+"hljs-number">204</span>
+                    },
+                    <span class=
+"hljs-attr">"additionalResponses"</span>: [
+                        {
+                            <span class=
+"hljs-attr">"description"</span>: <span class=
+"hljs-string">"TD with the given id not found"</span>,
+                            <span class=
+"hljs-attr">"contentType"</span>: <span class=
+"hljs-string">"application/problem+json"</span>,
+                            <span class=
+"hljs-attr">"htv:statusCodeValue"</span>: <span class=
+"hljs-number">404</span>
+                        }
+                    ]
+                }
+            ]
+        },
+        <span class="hljs-attr">"searchJSONPath"</span>: {
+            <span class=
+"hljs-attr">"description"</span>: <span class=
+"hljs-string">"JSONPath syntactic search.  This affordance is not normative and is provided for information only."</span>,
+            <span class="hljs-attr">"uriVariables"</span>: {
+                <span class="hljs-attr">"query"</span>: {
+                    <span class=
+"hljs-attr">"title"</span>: <span class=
+"hljs-string">"A valid JSONPath expression"</span>,
+                    <span class=
+"hljs-attr">"type"</span>: <span class=
+"hljs-string">"string"</span>
+                }
+            },
+            <span class="hljs-attr">"output"</span>: {
+                <span class=
+"hljs-attr">"description"</span>: <span class=
+"hljs-string">"The schema depends on the given query"</span>,
+                <span class="hljs-attr">"type"</span>: <span class=
+"hljs-string">"object"</span>
+            },
+            <span class="hljs-attr">"safe"</span>: <span class=
+"hljs-literal">true</span>,
+            <span class=
+"hljs-attr">"idempotent"</span>: <span class=
+"hljs-literal">true</span>,
+            <span class="hljs-attr">"forms"</span>: [
+                {
+                    <span class=
+"hljs-attr">"href"</span>: <span class=
+"hljs-string">"/search/jsonpath?query={query}"</span>,
+                    <span class=
+"hljs-attr">"htv:methodName"</span>: <span class=
+"hljs-string">"GET"</span>,
+                    <span class="hljs-attr">"response"</span>: {
+                        <span class=
+"hljs-attr">"description"</span>: <span class=
+"hljs-string">"Success response"</span>,
+                        <span class=
+"hljs-attr">"contentType"</span>: <span class=
+"hljs-string">"application/json"</span>,
+                        <span class=
+"hljs-attr">"htv:statusCodeValue"</span>: <span class=
+"hljs-number">200</span>
+                    },
+                    <span class=
+"hljs-attr">"additionalResponses"</span>: [
+                        {
+                            <span class=
+"hljs-attr">"description"</span>: <span class=
+"hljs-string">"JSONPath expression not provided or contains syntax errors"</span>,
+                            <span class=
+"hljs-attr">"contentType"</span>: <span class=
+"hljs-string">"application/problem+json"</span>,
+                            <span class=
+"hljs-attr">"htv:statusCodeValue"</span>: <span class=
+"hljs-number">400</span>
+                        }
+                    ]
+                }
+            ]
+        },
+        <span class="hljs-attr">"searchXPath"</span>: {
+            <span class=
+"hljs-attr">"description"</span>: <span class=
+"hljs-string">"XPath syntactic search.  This affordance is not normative and is provided for information only."</span>,
+            <span class="hljs-attr">"uriVariables"</span>: {
+                <span class="hljs-attr">"query"</span>: {
+                    <span class=
+"hljs-attr">"title"</span>: <span class=
+"hljs-string">"A valid XPath expression"</span>,
+                    <span class=
+"hljs-attr">"type"</span>: <span class=
+"hljs-string">"string"</span>
+                }
+            },
+            <span class="hljs-attr">"output"</span>: {
+                <span class=
+"hljs-attr">"description"</span>: <span class=
+"hljs-string">"The schema depends on the given query"</span>,
+                <span class="hljs-attr">"type"</span>: <span class=
+"hljs-string">"object"</span>
+            },
+            <span class="hljs-attr">"safe"</span>: <span class=
+"hljs-literal">true</span>,
+            <span class=
+"hljs-attr">"idempotent"</span>: <span class=
+"hljs-literal">true</span>,
+            <span class="hljs-attr">"forms"</span>: [
+                {
+                    <span class=
+"hljs-attr">"href"</span>: <span class=
+"hljs-string">"/search/xpath?query={query}"</span>,
+                    <span class=
+"hljs-attr">"htv:methodName"</span>: <span class=
+"hljs-string">"GET"</span>,
+                    <span class="hljs-attr">"response"</span>: {
+                        <span class=
+"hljs-attr">"description"</span>: <span class=
+"hljs-string">"Success response"</span>,
+                        <span class=
+"hljs-attr">"contentType"</span>: <span class=
+"hljs-string">"application/json"</span>,
+                        <span class=
+"hljs-attr">"htv:statusCodeValue"</span>: <span class=
+"hljs-number">200</span>
+                    },
+                    <span class=
+"hljs-attr">"additionalResponses"</span>: [
+                        {
+                            <span class=
+"hljs-attr">"description"</span>: <span class=
+"hljs-string">"XPath expression not provided or contains syntax errors"</span>,
+                            <span class=
+"hljs-attr">"contentType"</span>: <span class=
+"hljs-string">"application/problem+json"</span>,
+                            <span class=
+"hljs-attr">"htv:statusCodeValue"</span>: <span class=
+"hljs-number">400</span>
+                        }
+                    ]
+                }
+            ]
+        },
+        <span class="hljs-attr">"searchSPARQL"</span>: {
+            <span class=
+"hljs-attr">"description"</span>: <span class=
+"hljs-string">"SPARQL semantic search"</span>,
+            <span class="hljs-attr">"uriVariables"</span>: {
+                <span class="hljs-attr">"query"</span>: {
+                    <span class=
+"hljs-attr">"title"</span>: <span class=
+"hljs-string">"A valid SPARQL 1.1. query"</span>,
+                    <span class=
+"hljs-attr">"type"</span>: <span class=
+"hljs-string">"string"</span>
+                }
+            },
+            <span class="hljs-attr">"output"</span>: {
+                <span class=
+"hljs-attr">"description"</span>: <span class=
+"hljs-string">"The schema depends on the given query"</span>,
+                <span class="hljs-attr">"type"</span>: <span class=
+"hljs-string">"object"</span>
+            },
+            <span class="hljs-attr">"safe"</span>: <span class=
+"hljs-literal">true</span>,
+            <span class=
+"hljs-attr">"idempotent"</span>: <span class=
+"hljs-literal">true</span>,
+            <span class="hljs-attr">"forms"</span>: [
+                {
+                    <span class=
+"hljs-attr">"href"</span>: <span class=
+"hljs-string">"/search/sparql?query={query}"</span>,
+                    <span class=
+"hljs-attr">"htv:methodName"</span>: <span class=
+"hljs-string">"GET"</span>,
+                    <span class="hljs-attr">"response"</span>: {
+                        <span class=
+"hljs-attr">"description"</span>: <span class=
+"hljs-string">"Success response"</span>,
+                        <span class=
+"hljs-attr">"contentType"</span>: <span class=
+"hljs-string">"application/json"</span>,
+                        <span class=
+"hljs-attr">"htv:statusCodeValue"</span>: <span class=
+"hljs-number">200</span>
+                    },
+                    <span class=
+"hljs-attr">"additionalResponses"</span>: [
+                        {
+                            <span class=
+"hljs-attr">"description"</span>: <span class=
+"hljs-string">"SPARQL query not provided or contains syntax errors"</span>,
+                            <span class=
+"hljs-attr">"contentType"</span>: <span class=
+"hljs-string">"application/problem+json"</span>,
+                            <span class=
+"hljs-attr">"htv:statusCodeValue"</span>: <span class=
+"hljs-number">400</span>
+                        }
+                    ]
+                },
+                {
+                    <span class=
+"hljs-attr">"href"</span>: <span class=
+"hljs-string">"/search/sparql"</span>,
+                    <span class=
+"hljs-attr">"htv:methodName"</span>: <span class=
+"hljs-string">"POST"</span>,
+                    <span class="hljs-attr">"response"</span>: {
+                        <span class=
+"hljs-attr">"description"</span>: <span class=
+"hljs-string">"Success response"</span>,
+                        <span class=
+"hljs-attr">"contentType"</span>: <span class=
+"hljs-string">"application/json"</span>,
+                        <span class=
+"hljs-attr">"htv:statusCodeValue"</span>: <span class=
+"hljs-number">200</span>
+                    },
+                    <span class=
+"hljs-attr">"additionalResponses"</span>: [
+                        {
+                            <span class=
+"hljs-attr">"description"</span>: <span class=
+"hljs-string">"SPARQL query not provided or contains syntax errors"</span>,
+                            <span class=
+"hljs-attr">"contentType"</span>: <span class=
+"hljs-string">"application/problem+json"</span>,
+                            <span class=
+"hljs-attr">"htv:statusCodeValue"</span>: <span class=
+"hljs-number">400</span>
+                        }
+                    ]
+                }
+            ]
+        }
+    },
+    <span class="hljs-attr">"events"</span>: {
+        <span class="hljs-attr">"thingCreated"</span>: {
+            <span class=
+"hljs-attr">"description"</span>: <span class=
+"hljs-string">"Registration of Thing Descriptions inside the directory"</span>,
+            <span class="hljs-attr">"uriVariables"</span>: {
+                <span class="hljs-attr">"diff"</span>: {
+                    <span class=
+"hljs-attr">"description"</span>: <span class=
+"hljs-string">"Receive the full created TD as event data"</span>,
+                    <span class=
+"hljs-attr">"type"</span>: <span class=
+"hljs-string">"boolean"</span>
+                }
+            },
+            <span class="hljs-attr">"data"</span>: {
+                <span class=
+"hljs-attr">"title"</span>: <span class="hljs-string">"Partial/Full TD"</span>,
+                <span class="hljs-attr">"type"</span>: <span class=
+"hljs-string">"object"</span>
+            },
+            <span class="hljs-attr">"forms"</span>: [
+                {
+                    <span class=
+"hljs-attr">"op"</span>: <span class=
+"hljs-string">"subscribeevent"</span>,
+                    <span class=
+"hljs-attr">"href"</span>: <span class=
+"hljs-string">"/events/thing_created{?diff}"</span>,
+                    <span class=
+"hljs-attr">"subprotocol"</span>: <span class=
+"hljs-string">"sse"</span>,
+                    <span class="hljs-attr">"htv:headers"</span>: [
+                        {
+                            <span class=
+"hljs-attr">"description"</span>: <span class=
+"hljs-string">"ID of the last event for reconnection"</span>,
+                            <span class=
+"hljs-attr">"htv:fieldName"</span>: <span class=
+"hljs-string">"Last-Event-ID"</span>
+                        }
+                    ],
+                    <span class="hljs-attr">"response"</span>: {
+                        <span class=
+"hljs-attr">"contentType"</span>: <span class=
+"hljs-string">"text/event-stream"</span>
+                    }
+                }
+            ]
+        },
+        <span class="hljs-attr">"thingUpdated"</span>: {
+            <span class=
+"hljs-attr">"description"</span>: <span class=
+"hljs-string">"Updates to Thing Descriptions within the directory"</span>,
+            <span class="hljs-attr">"uriVariables"</span>: {
+                <span class="hljs-attr">"diff"</span>: {
+                    <span class=
+"hljs-attr">"description"</span>: <span class=
+"hljs-string">"Include TD changes inside event data"</span>,
+                    <span class=
+"hljs-attr">"type"</span>: <span class=
+"hljs-string">"boolean"</span>
+                }
+            },
+            <span class="hljs-attr">"data"</span>: {
+                <span class=
+"hljs-attr">"title"</span>: <span class="hljs-string">"Partial TD"</span>,
+                <span class="hljs-attr">"type"</span>: <span class=
+"hljs-string">"object"</span>,
+                <span class=
+"hljs-attr">"contentMediaType"</span>: <span class=
+"hljs-string">"application/merge-patch+json"</span>
+            },
+            <span class="hljs-attr">"forms"</span>: [
+                {
+                    <span class=
+"hljs-attr">"op"</span>: <span class=
+"hljs-string">"subscribeevent"</span>,
+                    <span class=
+"hljs-attr">"href"</span>: <span class=
+"hljs-string">"/events/thing_updated{?diff}"</span>,
+                    <span class=
+"hljs-attr">"subprotocol"</span>: <span class=
+"hljs-string">"sse"</span>,
+                    <span class="hljs-attr">"htv:headers"</span>: [
+                        {
+                            <span class=
+"hljs-attr">"description"</span>: <span class=
+"hljs-string">"ID of the last event for reconnection"</span>,
+                            <span class=
+"hljs-attr">"htv:fieldName"</span>: <span class=
+"hljs-string">"Last-Event-ID"</span>
+                        }
+                    ],
+                    <span class="hljs-attr">"response"</span>: {
+                        <span class=
+"hljs-attr">"contentType"</span>: <span class=
+"hljs-string">"text/event-stream"</span>
+                    }
+                }
+            ]
+        },
+        <span class="hljs-attr">"thingDeleted"</span>: {
+            <span class=
+"hljs-attr">"description"</span>: <span class=
+"hljs-string">"Deletion of Thing Descriptions from the directory"</span>,
+            <span class="hljs-attr">"data"</span>: {
+                <span class=
+"hljs-attr">"title"</span>: <span class="hljs-string">"Partial TD"</span>,
+                <span class="hljs-attr">"type"</span>: <span class=
+"hljs-string">"object"</span>
+            },
+            <span class="hljs-attr">"forms"</span>: [
+                {
+                    <span class=
+"hljs-attr">"op"</span>: <span class=
+"hljs-string">"subscribeevent"</span>,
+                    <span class=
+"hljs-attr">"href"</span>: <span class=
+"hljs-string">"/events/thing_deleted"</span>,
+                    <span class=
+"hljs-attr">"subprotocol"</span>: <span class=
+"hljs-string">"sse"</span>,
+                    <span class="hljs-attr">"htv:headers"</span>: [
+                        {
+                            <span class=
+"hljs-attr">"description"</span>: <span class=
+"hljs-string">"ID of the last event for reconnection"</span>,
+                            <span class=
+"hljs-attr">"htv:fieldName"</span>: <span class=
+"hljs-string">"Last-Event-ID"</span>
+                        }
+                    ],
+                    <span class="hljs-attr">"response"</span>: {
+                        <span class=
+"hljs-attr">"contentType"</span>: <span class=
+"hljs-string">"text/event-stream"</span>
+                    }
+                }
+            ]
+        }
+    }
+}
+</code>
+</pre>
+</section>
+</section>
+</section>
+</section>
+<section id="security-considerations">
+<div class="header-wrapper">
+<h2 id="x8-security-considerations">
+<bdi class="secno">
+8.
+</bdi>
+Security
+Considerations
+</h2>
+<a class="self-link" href="#security-considerations" aria-label= "Permalink for Section 8.">
+</a>
+</div>
+<p>
+Security
+is
+a
+cross-cutting
+issue
+that
+needs
+to
+be
+considered
+in
+all
+WoT
+building
+blocks
+and
+WoT
+implementations.
+This
+chapter
+summarizes
+some
+general
+issues
+and
+guidelines
+to
+help
+preserve
+the
+security
+of
+concrete
+WoT
+discovery
+implementations.
+For
+a
+more
+detailed
+and
+complete
+analysis
+of
+both
+security
+and
+privacy
+issues,
+see
+the
+<em>
+WoT
+Security
+and
+Privacy
+Guidelines
+</em>
+specification
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href= "#bib-wot-security" title= "Web of Things (WoT) Security and Privacy Guidelines">
+WOT-SECURITY
+</a>
+</cite>
+].
+WoT
+Thing
+and
+WoT
+TDDs
+are
+also
+web
+services
+and
+should
+be
+implemented
+using
+best
+practices
+for
+web
+services.
+In
+addition
+to
+the
+specific
+security
+considerations
+below,
+the
+security
+risks
+and
+mitigations
+discussed
+in
+guides
+such
+as
+the
+OWASP
+Top
+10
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href= "#bib-owasp-top-10" title="OWASP Top Ten">
+OWASP-Top-10
+</a>
+</cite>
+]
+should
+be
+evaluated,
+and
+if
+applicable,
+addressed.
+</p>
+<section id="security-consideration-dos">
+<div class="header-wrapper">
+<h3 id="x8-1-denial-of-service">
+<bdi class="secno">
+8.1
+</bdi>
+Denial
+of
+Service
+</h3>
+<a class="self-link" href="#security-consideration-dos" aria-label= "Permalink for Section 8.1">
+</a>
+</div>
+<p>
+Certain
+functions
+of
+the
+directory
+service,
+in
+particular
+search
+queries,
+may
+require
+significant
+resources
+to
+execute
+and
+this
+fact
+can
+be
+used
+to
+launch
+denial
+of
+service
+(DoS)
+attacks
+against
+WoT
+Thing
+Description
+Directory
+services.
+In
+such
+an
+attack
+a
+WoT
+Directory
+would
+be
+overloaded
+by
+requests
+from
+the
+attacker
+and
+unable
+to
+service
+other
+requests.
+</p>
+<dl>
+<dt>
+Mitigations:
+</dt>
+<dd>
+<ul>
+<li>
+A
+WoT
+Thing
+Description
+Directory
+implementation
+should
+limit
+the
+number
+of
+queries
+per
+unit
+time
+from
+the
+same
+requestor.
+</li>
+<li>
+A
+WoT
+Thing
+Description
+Directory
+implementation
+should
+limit
+the
+complexity
+of
+queries
+(for
+example,
+the
+total
+length
+of
+the
+query
+expression
+or
+its
+depth).
+</li>
+<li>
+A
+WoT
+Thing
+Description
+Directory
+implementation
+should
+use
+a
+watchdog
+timer
+to
+abort
+queries
+that
+take
+more
+than
+a
+certain
+maximum
+(implementation-configurable)
+amount
+of
+time.
+</li>
+</ul>
+</dd>
+</dl>
+</section>
+<section id="security-consideration-amp-ddos">
+<div class="header-wrapper">
+<h3 id="x8-2-amplification-and-distributed-denial-of-service">
+<bdi class="secno">
+8.2
+</bdi>
+Amplification
+and
+Distributed
+Denial
+of
+Service
+</h3>
+<a class="self-link" href="#security-consideration-amp-ddos" aria-label="Permalink for Section 8.2">
+</a>
+</div>
+<p>
+It
+may
+also
+be
+possible
+to
+use
+elements
+of
+WoT
+Discovery
+mechanisms
+to
+launch
+distributed
+denial
+of
+service
+(DDoS)
+attacks
+against
+other
+targets.
+In
+such
+an
+attack
+the
+WoT
+Discovery
+service
+itself
+is
+not
+the
+target.
+Instead,
+an
+aspect
+of
+the
+WoT
+Discovery
+service
+would
+be
+exploited
+to
+generate
+amplified
+network
+traffic
+that
+overloads
+a
+third
+party,
+the
+actual
+target.
+Such
+an
+attack
+has
+two
+requirements:
+first,
+the
+ability
+to
+redirect
+traffic
+to
+a
+third
+party,
+and
+second,
+an
+intermediary
+service
+that
+can
+be
+exploited
+to
+amplify
+network
+traffic
+from
+the
+attacker.
+Redirection
+of
+network
+traffic
+is
+possible
+in
+some
+protocols,
+such
+as
+unsecured
+CoAP,
+by
+modifying
+source
+information
+in
+headers.
+Amplification
+is
+possible
+by
+taking
+advantage
+of
+three
+multiplicative
+factors:
+the
+ratio
+of
+request
+to
+response
+payload
+sizes,
+use
+of
+"observe"
+in
+protocols
+like
+CoAP
+(which
+can
+give
+multiple
+results
+for
+one
+request),
+and
+use
+of
+multicast
+(which
+can
+allow
+multiple
+servers
+to
+respond
+to
+one
+request).
+Services
+which
+do
+not
+support
+authentication
+are
+ideal
+intermediaries
+for
+such
+an
+indirect
+attack.
+Unfortunately,
+the
+Introduction
+mechanisms
+for
+WoT
+Discovery
+are
+meant
+to
+provide
+open
+access
+mechanisms
+to
+initiate
+discovery
+and
+might
+be
+exploited
+for
+this
+purpose.
+</p>
+<dl>
+<dt>
+Mitigations:
+</dt>
+<dd>
+<ul>
+<li>
+<span class="rfc2119-assertion" id= "sec-tdd-intro-no-observe">
+Open
+implementations
+of
+Introduction
+mechanisms
+<em class="rfc2119">
+SHOULD
+NOT
+</em>
+support
+observe
+or
+similar
+extended
+result
+subprotocols.
+</span>
+</li>
+<li>
+Open
+implementations
+of
+Introduction
+mechanisms
+should
+not
+respond
+to
+multicast
+requests
+unless
+this
+is
+absolutely
+required
+by
+the
+protocol.
+If
+support
+for
+multicast
+is
+required,
+in
+the
+case
+of
+CoAP,
+the
+observations
+made
+in
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href="#bib-amplification-attacks" title= "Amplification Attacks Using the Constrained Application Protocol (CoAP)">
+AMPLIFICATION-ATTACKS
+</a>
+</cite>
+]
+are
+relevant,
+since
+the
+number
+of
+servers
+that
+might
+respond
+to
+a
+multicast
+request
+during
+discovery
+will
+generally
+not
+be
+known
+in
+advance.
+</li>
+<li>
+Limit
+the
+size
+of
+responses
+to
+the
+minimum.
+The
+total
+size
+of
+responses
+to
+an
+Introduction
+on
+the
+public
+internet
+(outside
+of
+a
+protected
+local
+network)
+should
+be
+less
+than
+3x
+the
+size
+of
+the
+total
+size
+of
+request,
+and
+this
+should
+include
+any
+error
+responses.
+This
+is
+consistent
+with
+DDOS
+mitigations
+in
+[
+<cite>
+<a class= "bibref" data-link-type="biblio" href="#bib-rfc9000" title= "QUIC: A UDP-Based Multiplexed and Secure Transport">
+RFC9000
+</a>
+</cite>
+]
+(QUIC)
+and
+HTTP/3.
+Here
+"total
+size"
+includes
+any
+headers
+required
+by
+the
+protocol
+itself,
+as
+well
+as
+padding
+in
+the
+request
+to
+allow
+for
+a
+larger
+response.
+</li>
+<li>
+Introductions
+should
+rate-limit
+responses
+to
+any
+particular
+request
+source.
+</li>
+<li>
+<span class="rfc2119-assertion" id= "sec-tdd-intro-no-ext">
+Introduction
+mechanisms
+on
+a
+segmented
+network
+behind
+a
+firewall
+(e.g.
+a
+LAN)
+<em class="rfc2119">
+SHOULD
+NOT
+</em>
+respond
+to
+requests
+that
+are
+(apparently)
+from
+outside
+that
+LAN.
+</span>
+</li>
+</ul>
+Of
+particular
+concern
+are
+Introduction
+mechanisms
+that
+can
+return
+multiple
+results,
+such
+as
+CoRE-RD
+and
+DID.
+It
+may
+be
+necessary
+to
+use
+authentication/authorization
+on
+such
+Introduction
+mechanisms
+as
+well
+if
+the
+other
+mitigations
+above
+are
+not
+sufficient.
+A
+recommended
+alternative
+is
+to
+move
+multiple
+results
+from
+such
+Introductions
+into
+a
+WoT
+TDD,
+which
+can
+then
+be
+protected
+by
+appropriate
+authentication
+and
+authorization
+measures.
+Then
+the
+open
+Introduction
+mechanism
+only
+has
+to
+return
+one
+result,
+the
+URL
+of
+the
+TDD.
+Introduction
+mechanisms
+that
+are
+visible
+on
+the
+open
+internet
+should
+be
+especially
+careful
+to
+implement
+the
+above
+mitigations,
+and
+perhaps
+avoid
+Introduction
+mechanisms
+that
+can
+return
+multiple
+URLs
+completely.
+</dd>
+</dl>
+</section>
+<section id="security-consideration-lan-self-discovery">
+<div class="header-wrapper">
+<h3 id="x8-3-self-discovery-on-lans">
+<bdi class="secno">
+8.3
+</bdi>
+Self-Discovery
+on
+LANs
+</h3>
+<a class="self-link" href= "#security-consideration-lan-self-discovery" aria-label= "Permalink for Section 8.3">
+</a>
+</div>
+<p>
+On
+a
+LAN,
+certificates
+and
+browsers
+may
+not
+be
+able
+to
+property
+set
+up
+TLS
+for
+HTTPS
+because
+browsers
+expect
+certificates
+pointing
+to
+a
+publicly-visible
+URL.
+Using
+HTTP
+is
+common
+practice
+inside
+LANs
+but
+in
+combination
+with
+self-description
+it
+means
+that
+WoT
+Things
+would
+be
+essentially
+be
+making
+TDs
+visible
+to
+everyone
+with
+access
+to
+the
+private
+LAN.
+Even
+if
+security
+mechanisms
+such
+as
+HTTP
+passwords
+were
+used,
+these
+are
+not
+effective
+(they
+can
+be
+easily
+discovered
+by
+a
+traffic
+analyser)
+without
+transport
+security.
+</p>
+<dl>
+<dt>
+Mitigations:
+</dt>
+<dd>
+<p>
+<span class="rfc2119-assertion" id="sec-self-psk">
+PSK
+(pre-shared
+keys)
+<em class="rfc2119">
+SHOULD
+</em>
+be
+used
+if
+possible
+on
+LANs,
+meaning
+one
+of
+the
+ciphersuites
+in
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href= "#bib-rfc4279" title= "Pre-Shared Key Ciphersuites for Transport Layer Security (TLS)">
+RFC4279
+</a>
+</cite>
+].
+</span>
+This
+does
+require
+that
+Things
+are
+assigned
+PSKs
+in
+a
+common
+security
+domain,
+which
+is
+typically
+done
+by
+following
+an
+onboarding
+process.
+Unfortunately,
+specific
+onboarding
+processes
+are
+currently
+out
+of
+scope
+of
+the
+WoT
+specifications.
+</p>
+<p>
+An
+alternative
+is
+to
+depend
+on
+local
+network
+security
+(i.e.
+WEP).
+This
+is
+not
+the
+best
+solution
+from
+a
+security
+or
+privacy
+point
+of
+view
+but
+may
+be
+acceptable
+in
+some
+contexts.
+Note
+however
+that
+all
+users
+with
+access
+to
+the
+network
+would
+in
+turn
+have
+access
+to
+all
+TDs
+via
+self-description.
+<span class="rfc2119-assertion" id="sec-self-segment">
+If
+Things
+cannot
+be
+individually
+secured
+with
+transport
+security
+and
+authentication
+and
+authorization,
+a
+separate
+network
+<em class="rfc2119">
+SHOULD
+</em>
+be
+set
+up,
+i.e.
+with
+an
+alternative
+SSID,
+and
+used
+only
+for
+IoT
+devices.
+</span>
+Using
+a
+segmented
+network
+reduces
+the
+need
+for
+distributing
+the
+password
+to
+this
+network
+to
+those
+who
+need
+access
+to
+the
+set
+of
+IoT
+devices
+connected
+to
+it.
+</p>
+<p>
+Another
+alternative
+is
+to
+use
+a
+reverse
+proxy
+service
+based
+in
+the
+cloud.
+Secure
+setup
+can
+be
+accomplished
+if
+the
+IoT
+device
+has
+access
+to
+the
+cloud,
+since
+the
+proxy
+server
+can
+have
+a
+public
+URL
+and
+the
+initial
+connection
+can
+use
+HTTPS,
+then
+open
+a
+secure
+tunnel
+over
+a
+websocket.
+The
+proxy
+can
+in
+turn
+re-expose
+a
+secure
+endpoint,
+and
+possible
+add
+authentication.
+The
+disadvantages
+of
+this
+approach
+including
+depending
+on
+an
+external
+cloud
+service
+and
+the
+need
+to
+expose
+an
+external
+access
+point
+(which
+is
+itself
+a
+security
+risk).
+The
+first
+disadvantage
+can
+be
+addressed
+by
+hosting
+the
+proxy
+service
+locally
+and
+exposing
+a
+public
+URL
+using
+e.g.
+dynamic
+DNS
+if
+the
+local
+server
+is
+connected
+through
+an
+ISP.
+If
+Things
+cannot
+be
+individually
+secured
+with
+transport
+security
+and
+authentication
+and
+authorization,
+then
+they
+may
+be
+made
+available
+for
+general
+access
+via
+a
+proxy
+that
+can
+provide
+suitable
+access
+controls.
+</p>
+</dd>
+</dl>
+</section>
+</section>
+<section id="privacy-considerations">
+<div class="header-wrapper">
+<h2 id="x9-privacy-considerations">
+<bdi class="secno">
+9.
+</bdi>
+Privacy
+Considerations
+</h2>
+<a class="self-link" href="#privacy-considerations" aria-label= "Permalink for Section 9.">
+</a>
+</div>
+<p>
+Privacy
+is
+a
+cross-cutting
+issue
+that
+needs
+to
+be
+considered
+in
+all
+WoT
+building
+blocks
+and
+WoT
+implementations.
+This
+chapter
+summarizes
+some
+general
+issues
+and
+guidelines
+to
+help
+preserve
+the
+privacy
+of
+concrete
+WoT
+discovery
+implementations.
+For
+a
+more
+detailed
+and
+complete
+analysis
+of
+both
+security
+and
+privacy
+issues,
+see
+the
+<em>
+WoT
+Security
+and
+Privacy
+Guidelines
+</em>
+specification
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href= "#bib-wot-security" title= "Web of Things (WoT) Security and Privacy Guidelines">
+WOT-SECURITY
+</a>
+</cite>
+].
+</p>
+<p>
+The
+WoT
+discovery
+architecture
+is
+designed
+to
+avoid
+a
+dependence
+on
+the
+privacy
+of
+existing
+discovery
+schemes
+by
+using
+a
+two-phase
+approach
+and
+allowing
+for
+the
+enforcement
+of
+authorization
+before
+metadata
+release.
+However
+several
+privacy
+risks
+still
+exist.
+These
+are
+listed
+below
+along
+with
+possible
+mitigations.
+The
+level
+of
+risk
+to
+privacy
+in
+particular
+depends
+on
+the
+use
+case
+and
+whether
+there
+is
+a
+risk
+that
+information
+related
+to
+a
+person
+might
+be
+distributed
+in
+a
+fashion
+inconsistent
+with
+the
+privacy
+desires
+of
+that
+person.
+For
+privacy
+we
+distinguish
+the
+following
+broad
+classes
+of
+use
+case
+scenarios:
+</p>
+<dl>
+<dt>
+Institutional
+</dt>
+<dd>
+Both
+the
+Things
+producing
+metadata
+and
+the
+Consumers
+of
+that
+metadata
+are
+owned
+and
+controlled
+by
+an
+institution
+or
+representatives
+of
+an
+institution.
+Example:
+Automation
+in
+a
+factory
+where
+a
+control
+system
+is
+accessing
+the
+state
+of
+an
+assembly
+line
+in
+order
+to
+evaluate
+quality.
+</dd>
+<dt>
+Service
+</dt>
+<dd>
+The
+Things
+producing
+metadata
+are
+owned
+and
+controlled
+by
+an
+institution
+or
+representatives
+of
+an
+institution
+while
+the
+consumers
+are
+individuals.
+Example:
+driver
+of
+an
+electric
+vehicle
+accessing
+the
+TD
+for
+a
+charge
+station
+in
+order
+to
+check
+status
+of
+a
+charge.
+</dd>
+<dt>
+Personal
+</dt>
+<dd>
+Both
+the
+Things
+producing
+metadata
+and
+the
+Consumers
+of
+that
+metadata
+are
+owned
+and
+controlled
+by
+the
+same
+individual.
+Example:
+A
+smart
+home
+control
+system
+for
+charging
+an
+electric
+car
+from
+home-attached
+solar
+panels,
+both
+home
+and
+car
+owned
+by
+the
+same
+person.
+</dd>
+<dt>
+Personal
+Peer-to-Peer
+</dt>
+<dd>
+The
+Things
+producing
+metadata
+and
+the
+Consumers
+of
+that
+metadata
+are
+owned
+and
+controlled
+by
+different
+individuals.
+Example:
+A
+smart
+home
+control
+system
+for
+charging
+a
+guest's
+electric
+car
+from
+home-attached
+solar
+panels.
+</dd>
+<dt>
+Institutional
+Peer-to-Peer
+</dt>
+<dd>
+The
+Things
+producing
+metadata
+and
+the
+Consumers
+of
+that
+metadata
+are
+owned
+and
+controlled
+by
+different
+institutions.
+Example:
+A
+utility
+provides
+and
+manages
+power
+delivered
+to
+a
+factory,
+and
+the
+factory
+provides
+an
+interface
+for
+the
+utility
+to
+negotiate
+on-demand
+power
+usage
+reductions.
+</dd>
+<dt>
+Client
+</dt>
+<dd>
+The
+Things
+producing
+metadata
+are
+owned
+and
+controlled
+by
+an
+individual
+while
+the
+consumers
+are
+an
+institution
+or
+representatives
+of
+an
+institution.
+Example:
+A
+personal
+electric
+vehicle
+exposes
+an
+interface
+to
+a
+public
+charging
+station
+so
+that
+the
+charging
+station
+can
+evaluate
+the
+charge
+status
+of
+the
+vehicle.
+</dd>
+</dl>
+<p>
+All
+of
+these
+in
+fact
+carry
+privacy
+risks.
+Even
+in
+the
+case
+of
+factory
+automation,
+there
+is
+the
+chance
+that
+data
+about
+employee
+performance
+would
+be
+captured
+and
+would
+have
+to
+be
+managed
+appropriately.
+</p>
+<p>
+In
+the
+following
+we
+make
+frequent
+reference
+to
+"tracking".
+This
+term
+covers
+multiple
+privacy
+risks,
+including
+location
+tracking
+and
+behavioral
+profiling.
+In
+general,
+the
+definition
+of
+"profiling"
+given
+in
+Article
+4
+of
+the
+GDPR
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href="#bib-gdpr-defs" title= "General Data Protection Regulation (GDPR) Article 4 - Definitions">
+GDPR-Defs
+</a>
+</cite>
+]
+is
+to
+be
+considered
+equivalent
+to
+"tracking"
+as
+used
+in
+this
+document.
+</p>
+<p>
+With
+these
+definitions
+and
+categories
+established,
+we
+will
+now
+discuss
+some
+specific
+privacy
+risks
+and
+potential
+mitigations.
+</p>
+<section id="privacy-consideration-location-tracking">
+<div class="header-wrapper">
+<h3 id="x9-1-location-tracking-and-profiling">
+<bdi class= "secno">
+9.1
+</bdi>
+Location
+Tracking
+and
+Profiling
+</h3>
+<a class="self-link" href= "#privacy-consideration-location-tracking" aria-label= "Permalink for Section 9.1">
+</a>
+</div>
+<p>
+A
+discovery
+service
+may
+potentially
+allow
+the
+approximate
+location
+of
+a
+person
+to
+be
+determined
+without
+their
+consent.
+This
+risk
+occurs
+in
+some
+specific
+circumstances
+which
+can
+be
+avoided
+or
+mitigated.
+It
+is
+also
+similar
+to
+the
+risk
+posed
+by
+other
+network
+services
+such
+as
+DHCP
+and
+DNS.
+</p>
+<p>
+For
+this
+risk
+to
+occur,
+there
+first
+has
+to
+be
+an
+IoT
+device
+that
+can
+be
+reliably
+associated
+with
+a
+person's
+location,
+such
+as
+a
+necessary
+medical
+device
+or
+a
+vehicle.
+Note
+that
+the
+risk
+only
+applies
+to
+personal
+use
+cases,
+not
+institutional
+ones.
+Secondly,
+the
+device
+has
+to
+be
+configured
+to
+register
+automatically
+with
+the
+nearest
+directory
+service.
+In
+this
+case,
+the
+location
+of
+the
+device
+can
+be
+inferred
+from
+the
+network
+range
+of
+the
+directory
+service
+and
+the
+location
+of
+the
+person
+inferred
+from
+the
+location
+of
+the
+device.
+</p>
+<p>
+There
+are
+a
+few
+variants
+of
+this:
+</p>
+<ul>
+<li>
+The
+TD
+or
+Thing
+could
+report
+actual
+location
+information
+so
+no
+inferencing
+by
+network
+range
+is
+needed;
+</li>
+<li>
+A
+directory
+could
+support
+actual
+search
+by
+location;
+</li>
+<li>
+Absence
+of
+a
+TD
+in
+a
+directory
+could
+reveal
+negative
+location
+information.
+For
+example,
+if
+a
+TD
+times
+out
+and
+is
+removed
+from
+a
+directory,
+that
+means
+the
+device
+has
+not
+been
+present
+for
+a
+while,
+which
+could
+be
+used
+to
+infer
+that
+a
+person
+is
+NOT
+in
+a
+particular
+location,
+e.g.
+not
+at
+home.
+</li>
+</ul>
+<p>
+Location
+tracking
+is
+not
+the
+only
+profiling
+risk.
+In
+general,
+"profiling"
+includes
+any
+mechanism
+used
+to
+evaluate
+information
+about
+a
+person,
+including
+economic
+status,
+health,
+preferences,
+interests,
+reliability,
+and
+behavior.
+Some
+of
+the
+metadata
+in
+a
+TD
+can
+be
+used
+to
+infer
+information
+of
+this
+kind
+if
+the
+described
+Thing
+can
+be
+associated
+with
+a
+person.
+Some
+of
+the
+mitigations
+below
+are
+also
+applicable
+to
+this
+more
+general
+definition
+of
+profiling.
+</p>
+<p>
+Some
+of
+these
+risks
+are
+shared
+by
+similar
+services.
+For
+example,
+DCHP
+automatically
+responds
+to
+requests
+for
+IP
+addresses
+on
+a
+local
+network,
+and
+devices
+typically
+provide
+an
+identifier
+(a
+MAC
+address)
+as
+part
+of
+this
+process,
+and
+the
+DHCP
+server
+maintains
+a
+registry.
+In
+theory,
+someone
+with
+access
+to
+the
+DHCP
+server
+in,
+say,
+a
+cafe,
+could
+use
+this
+information
+to
+track
+someone's
+phone
+and
+infer
+their
+location.
+</p>
+<dl>
+<dt>
+Mitigations:
+</dt>
+<dd>
+There
+are
+a
+few
+options
+to
+mitigate
+these
+risks:
+<ul>
+<li>
+To
+avoid
+location
+tracking
+and
+other
+forms
+of
+profiling,
+a
+WoT
+Thing
+associated
+with
+a
+person
+may
+disable
+registration
+with
+public
+directories.
+Registration
+would
+still
+be
+possible
+with
+personal
+directories,
+for
+example,
+a
+home
+gateway,
+but
+a
+user
+could
+disable
+registration
+at
+other
+locations.
+This
+has
+the
+disadvantage
+that
+functionality
+is
+lost:
+personal
+devices
+cannot
+be
+discovered
+in
+public
+locations.
+This
+could
+be
+addressed
+by
+having
+internet-accessible
+private
+discovery
+services.
+For
+example,
+the
+user's
+home
+gateway
+could
+provide
+an
+internet-accessible
+service,
+but
+with
+access
+control
+limiting
+use
+to
+authorized
+users.
+</li>
+<li>
+To
+avoid
+location
+tracking
+and
+other
+forms
+of
+profiling,
+a
+WoT
+Thing
+associated
+with
+a
+person
+should
+use
+anonymous
+TDs
+when
+registering
+with
+a
+public
+directories.
+In
+some
+cases,
+it
+may
+be
+possible
+to
+use
+anonymous
+TDs
+and
+omit
+explicit
+IDs
+from
+TDs
+submitted
+to
+a
+TDD.
+In
+this
+case
+the
+TDD
+will
+generate
+a
+local
+ID
+valid
+only
+in
+that
+TDD.
+This
+does,
+however,
+complicate
+update
+since
+the
+client
+needs
+to
+remember
+the
+local
+ID
+assigned
+by
+the
+TDD.
+Anonymous
+TDs
+also
+do
+not
+prevent
+tracking
+by
+other
+means,
+such
+as
+fingerprinting.
+</li>
+<li>
+To
+avoid
+location
+tracking
+and
+other
+forms
+of
+profiling,
+a
+WoT
+Thing
+associated
+with
+a
+person
+may
+periodically
+generate
+new
+IDs.
+Using
+fixed
+IDs
+makes
+it
+exceptionally
+easy
+to
+track
+devices.
+This
+problem
+also
+occurs
+in
+DHCP
+with
+MAC
+address
+and
+there
+is
+a
+similar
+partial
+mitigation:
+generate
+new
+random
+IDs
+periodically.
+There
+are
+however,
+a
+few
+issues.
+First
+of
+all,
+other
+identification
+information
+in
+the
+TD
+needs
+to
+be
+hidden.
+For
+example,
+client
+IDs
+issued
+by
+CSPs
+for
+API
+security
+should
+be
+omitted
+from
+TDs
+if
+they
+cannot
+be
+easily
+changed.
+Second,
+if
+the
+device
+generates
+a
+new
+ID,
+the
+user
+may
+still
+need
+to
+know
+the
+current
+ID
+to
+find
+the
+device
+via
+discovery.
+This
+can
+be
+accomplished
+however
+by
+generating
+new
+IDs
+using
+a
+deterministic
+cryptographic
+generator
+that
+is
+a
+function
+of
+the
+current
+time.
+However,
+note
+that
+regenerating
+IDs
+alone
+does
+not
+make
+tracking
+impossible
+since
+a
+TD
+might
+be
+fingerprinted.
+Also,
+updating
+an
+ID
+might
+be
+observable
+to
+the
+owner
+of
+the
+directory
+service,
+who
+could
+track
+and
+record
+the
+updated
+ID.
+Even
+if
+the
+TD
+is
+deleted
+and
+reinserted
+the
+association
+could
+be
+inferred.
+This
+is
+however
+exactly
+parallel
+to
+the
+situation
+with
+DHCP
+and
+rotation
+of
+MAC
+addresses.
+In
+general,
+however,
+generating
+new
+IDs
+at
+least
+for
+each
+service
+or
+person
+to
+which
+a
+TD
+is
+supplied
+makes
+it
+harder
+to
+connect
+registration
+events
+at
+different
+locations
+and
+times.
+It
+is
+also
+prudent
+to
+generate
+new
+identifiers
+upon
+major
+changes
+in
+configuration,
+such
+as
+unregistering
+from
+a
+local
+network
+or
+hub
+and
+registering
+with
+a
+new
+one
+(which
+typically
+indicates
+a
+change
+in
+ownership).
+There
+is
+a
+related
+issue
+with
+long-lived
+IP
+addresses
+which
+might
+need
+to
+be
+updated
+periodically
+to
+mitigate
+tracking.
+In
+the
+context
+of
+ipv6
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href= "#bib-rfc8981" title= "Temporary Address Extensions for Stateless Address Autoconfiguration in IPv6">
+RFC8981
+</a>
+</cite>
+]
+discusses
+this.
+Finally,
+there
+is
+a
+problem
+with
+devices
+that
+require
+immutable
+identifiers,
+e.g.
+medical
+devices
+in
+such
+jurisdictions.
+This
+is
+discussed
+in
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href="#bib-wot-thing-description11" title= "Web of Things (WoT) Thing Description 1.1">
+wot-thing-description11
+</a>
+</cite>
+],
+but
+in
+summary
+the
+problem
+can
+be
+avoided
+if
+such
+immutable
+identifiers
+are
+made
+available
+only
+as
+protected
+properties,
+e.g.
+via
+affordances
+requiring
+authentication,
+not
+in
+the
+TD,
+and
+the
+TD
+identifier
+itself
+(if
+used)
+is
+independent
+of
+the
+immutable
+identifier,
+and
+so
+can
+be
+made
+mutable.
+</li>
+<li>
+<span class="rfc2119-assertion" id= "priv-loc-priv-dir-access">
+To
+reduce
+the
+risk
+of
+negative
+location
+inferencing,
+access
+to
+private
+directories
+<em class= "rfc2119">
+SHOULD
+</em>
+be
+limited
+by
+using
+access
+controls.
+</span>
+If
+an
+attacker
+cannot
+access
+the
+service,
+they
+cannot
+retrieve
+information
+to
+infer
+location.
+Access
+rights
+provided
+to
+guests
+(e.g.
+for
+Peer-to-Peer
+Personal
+scenarios)
+should
+be
+appropriately
+time-limited.
+Use
+of
+long
+time-to-live
+values
+may
+be
+appropriate
+in
+other
+cases.
+In
+addition,
+TDs
+should
+be
+updated
+in
+a
+directory
+only
+when
+they
+change.
+For
+example,
+the
+TD
+for
+a
+car
+may
+only
+be
+updated
+when
+new
+car
+firmware
+is
+available
+providing
+new
+services,
+and
+the
+time-to-live
+might
+be
+set
+at
+one
+month
+(covering
+most
+absences).
+</li>
+<li>
+<span class="rfc2119-assertion" id= "priv-loc-explicit-care">
+When
+explicit
+location
+information
+is
+available,
+whether
+stored
+in
+a
+TD
+or
+available
+in
+a
+property,
+additional
+care
+<em class="rfc2119">
+SHOULD
+</em>
+be
+taken
+to
+only
+share
+the
+TD
+and/or
+access
+to
+the
+device
+with
+trusted
+partners,
+including
+directories.
+</span>
+If
+the
+TD
+must
+be
+shared
+with
+a
+public
+directory,
+the
+location
+information
+may
+be
+stripped.
+</li>
+</ul>
+</dd>
+</dl>
+</section>
+<section id="privacy-consideration-query-tracking">
+<div class="header-wrapper">
+<h3 id="x9-2-query-tracking">
+<bdi class="secno">
+9.2
+</bdi>
+Query
+Tracking
+</h3>
+<a class="self-link" href="#privacy-consideration-query-tracking" aria-label="Permalink for Section 9.2">
+</a>
+</div>
+<p>
+A
+directory
+service
+could
+potentially
+record
+and
+track
+queries
+by
+an
+individual,
+identifying
+that
+individual
+by
+their
+authenticated
+identity
+provided.
+Then
+the
+set
+of
+queries
+associated
+with
+an
+individual
+could
+be
+used
+to
+profile
+that
+individual,
+and
+specific
+queries
+may
+also
+reveal
+personal
+information
+about
+an
+individual.
+</p>
+<dl>
+<dt>
+Mitigations:
+</dt>
+<dd>
+<p>
+When
+accessing
+a
+public
+directory,
+like
+any
+other
+public
+web
+service,
+users
+and
+implementations
+should
+use
+an
+anonymous
+identity
+provider.
+In
+particular,
+OAuth2
+can
+provide
+tokens
+which
+don't
+identify
+specific
+individuals,
+they
+just
+assert
+access
+rights
+proven
+elsewhere.
+</p>
+</dd>
+</dl>
+</section>
+</section>
+<section id="performance-considerations" class="informative">
+<div class="header-wrapper">
+<h2 id="x10-performance-considerations">
+<bdi class= "secno">
+10.
+</bdi>
+Performance
+Considerations
+</h2>
+<a class="self-link" href="#performance-considerations" aria-label= "Permalink for Section 10.">
+</a>
+</div>
+<p>
+<em>
+This
+section
+is
+non-normative.
+</em>
+</p>
+<section id="perf-incremental-transfer">
+<div class="header-wrapper">
+<h3 id="x10-1-incremental-transfer">
+<bdi class="secno">
+10.1
+</bdi>
+Incremental
+Transfer
+</h3>
+<a class="self-link" href="#perf-incremental-transfer" aria-label= "Permalink for Section 10.1">
+</a>
+</div>
+<p>
+<a href="#dfn-td" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-td-46">
+TD
+</a>
+objects
+are
+not
+constrained
+in
+size.
+They
+may
+become
+expensive
+to
+process
+and
+transfer
+individually
+or
+collectively.
+A
+single
+TD
+or
+a
+list
+of
+TDs
+could
+be
+too
+large
+for
+a
+constrained
+device,
+serving
+its
+own
+TD
+to
+consumers,
+submitting
+it
+to
+a
+directory,
+or
+consuming
+other
+TDs.
+To
+meet
+such
+requirements,
+servers
+should
+support
+incremental
+transfer
+of
+payloads
+using
+protocol-specific
+mechanisms:
+</p>
+<ul>
+<li>
+HTTP/1.1
+servers
+should
+support
+<code>
+chunked
+</code>
+<a href= "https://datatracker.ietf.org/doc/html/rfc7230#section-3.3.1">
+Transfer-Encoding
+</a>
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href= "#bib-rfc7230" title= "Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">
+RFC7230
+</a>
+</cite>
+]
+to
+receive
+and
+server
+data
+incrementally.
+</li>
+<li>
+HTTP/2
+servers
+should
+handle
+the
+data
+incrementally
+using
+<a href= "https://datatracker.ietf.org/doc/html/rfc7540#section-4">
+HTTP
+Frames
+</a>
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href= "#bib-rfc7540" title= "Hypertext Transfer Protocol Version 2 (HTTP/2)">
+RFC7540
+</a>
+</cite>
+].
+The
+HTTP/1.1
+chunked
+transfer
+encoding
+is
+not
+supported
+in
+HTTP/2.
+</li>
+<li>
+CoAP
+servers
+must
+suppoert
+block-wise
+transfer
+[
+<cite>
+<a class= "bibref" data-link-type="biblio" href="#bib-rfc7959" title= "Block-Wise Transfers in the Constrained Application Protocol (CoAP)">
+RFC7959
+</a>
+</cite>
+]
+when
+relying
+on
+an
+unreliable
+transport
+protocol
+like
+UDP
+and
+should
+support
+it
+when
+using
+a
+reliable
+transport
+protocol
+like
+TCP
+or
+WebSockets
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href="#bib-rfc8323" title= "CoAP (Constrained Application Protocol) over TCP, TLS, and WebSockets">
+RFC8323
+</a>
+</cite>
+].
+</li>
+</ul>
+<p>
+Most
+HTTP
+servers
+and
+clients
+automatically
+process
+the
+data
+that
+is
+transferred
+in
+chunks.
+Memory-constrained
+clients
+should
+consider
+consuming
+the
+received
+data
+incrementally,
+instead
+of
+trying
+to
+load
+a
+whole
+object
+in
+memory
+for
+de-serialization.
+</p>
+</section>
+</section>
+<section id="iana-considerations" class="normative">
+<div class="header-wrapper">
+<h2 id="x11-iana-considerations">
+<bdi class="secno">
+11.
+</bdi>
+IANA
+Considerations
+</h2>
+<a class="self-link" href="#iana-considerations" aria-label= "Permalink for Section 11.">
+</a>
+</div>
+<section id="well-known-uri-suffix">
+<div class="header-wrapper">
+<h3 id="x11-1-well-known-uri-registration">
+<bdi class= "secno">
+11.1
+</bdi>
+Well-Known
+URI
+Registration
+</h3>
+<a class="self-link" href="#well-known-uri-suffix" aria-label= "Permalink for Section 11.1">
+</a>
+</div>
+<p>
+IANA
+will
+be
+asked
+to
+allocate
+the
+following
+value
+into
+the
+Well-Known
+URI
+defined
+in
+[
+<cite>
+<a class="bibref" data-link-type= "biblio" href="#bib-rfc8615" title= "Well-Known Uniform Resource Identifiers (URIs)">
+RFC8615
+</a>
+</cite>
+].
+</p>
+<ul>
+<li>
+URI
+suffix:
+<code>
+wot
+</code>
+</li>
+</ul>
+</section>
+<section id="service-name">
+<div class="header-wrapper">
+<h3 id="x11-2-service-name-registration">
+<bdi class= "secno">
+11.2
+</bdi>
+Service
+Name
+Registration
+</h3>
+<a class="self-link" href="#service-name" aria-label= "Permalink for Section 11.2">
+</a>
+</div>
+<p>
+IANA
+will
+be
+asked
+to
+allocate
+the
+following
+value
+into
+Service
+Name
+and
+Transport
+Protocol
+Port
+Number
+Registry
+defined
+in
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href= "#bib-rfc6335" title= "Internet Assigned Numbers Authority (IANA) Procedures for the Management of the Service Name and Transport Protocol Port Number Registry">
+RFC6335
+</a>
+</cite>
+].
+</p>
+<ul>
+<li>
+Service
+Name:
+<code>
+wot
+</code>
+</li>
+<li>
+Transport
+Protocol:
+TCP,
+UDP
+</li>
+<li>
+Description:
+Service
+name
+to
+search
+for
+the
+Thing
+Description
+of
+a
+Thing
+or
+a
+Thing
+Description
+Directory
+in
+the
+<abbr title= "World Wide Web Consortium">
+W3C
+</abbr>
+Web
+of
+Things
+</li>
+<li>
+Port
+Number:
+N/A
+</li>
+<li>
+Assignment
+notes:
+We
+use
+<code>
+_directory
+</code>
+subtype
+for
+a
+Thing
+Description
+Directory.
+</li>
+</ul>
+</section>
+<section id="core-resource-type">
+<div class="header-wrapper">
+<h3 id="x11-3-core-resource-types-registration">
+<bdi class= "secno">
+11.3
+</bdi>
+CoRE
+Resource
+Types
+Registration
+</h3>
+<a class="self-link" href="#core-resource-type" aria-label= "Permalink for Section 11.3">
+</a>
+</div>
+<p>
+IANA
+will
+be
+asked
+to
+allocate
+the
+following
+values
+into
+the
+Resource
+Type
+(
+<code>
+rt=
+</code>
+)
+Link
+Target
+Attribute
+Values
+sub-registry
+of
+the
+Constrained
+Restful
+Environments
+(CoRE)
+Parameters
+registry
+defined
+in
+[
+<cite>
+<a class="bibref" data-link-type="biblio" href="#bib-rfc6690" title= "Constrained RESTful Environments (CoRE) Link Format">
+RFC6690
+</a>
+</cite>
+].
+</p>
+<table class="def">
+<thead>
+<tr>
+<th>
+Value
+</th>
+<th>
+Description
+</th>
+<th>
+Reference
+</th>
+</tr>
+</thead>
+<tbody>
+<tr>
+<td>
+<code>
+wot.thing
+</code>
+</td>
+<td>
+Thing
+Description
+of
+a
+Thing
+</td>
+<td>
+<a href="#introduction-core-rd-sec" data-matched-text= "[[[#introduction-core-rd-sec]]]" class="sec-ref">
+<bdi class= "secno">
+6.4
+</bdi>
+CoRE
+Link
+Format
+and
+CoRE
+Resource
+Directory
+</a>
+</td>
+</tr>
+<tr>
+<td>
+<code>
+wot.directory
+</code>
+</td>
+<td>
+Thing
+Description
+of
+a
+<a href= "#dfn-wot-thing-description-directory" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-wot-thing-description-directory-23">
+Thing
+Description
+Directory
+</a>
+</td>
+<td>
+<a href="#introduction-core-rd-sec" data-matched-text= "[[[#introduction-core-rd-sec]]]" class="sec-ref">
+<bdi class= "secno">
+6.4
+</bdi>
+CoRE
+Link
+Format
+and
+CoRE
+Resource
+Directory
+</a>
+</td>
+</tr>
+</tbody>
+</table>
+</section>
+</section>
+<section id="other-name-considerations" class="normative">
+<div class="header-wrapper">
+<h2 id="x12-other-name-registration-considerations">
+<bdi class= "secno">
+12.
+</bdi>
+Other
+Name
+Registration
+Considerations
+</h2>
+<a class="self-link" href="#other-name-considerations" aria-label= "Permalink for Section 12.">
+</a>
+</div>
+<section id="did-service-name">
+<div class="header-wrapper">
+<h3 id="x12-1-did-service-name-registration">
+<bdi class= "secno">
+12.1
+</bdi>
+DID
+Service
+Name
+Registration
+</h3>
+<a class="self-link" href="#did-service-name" aria-label= "Permalink for Section 12.1">
+</a>
+</div>
+<p>
+The
+following
+values
+will
+be
+allocated
+for
+the
+Service
+Type
+used
+in
+DID
+Documents.
+</p>
+<table class="def">
+<thead>
+<tr>
+<th>
+Value
+</th>
+<th>
+Description
+</th>
+<th>
+Reference
+</th>
+</tr>
+</thead>
+<tbody>
+<tr>
+<td>
+<code>
+WotThing
+</code>
+</td>
+<td>
+Thing
+Description
+of
+a
+Thing
+</td>
+<td>
+<a href="#introduction-did-sec" data-matched-text= "[[[#introduction-did-sec]]]" class="sec-ref">
+<bdi class= "secno">
+6.5
+</bdi>
+DID
+Documents
+</a>
+</td>
+</tr>
+<tr>
+<td>
+<code>
+WotDirectory
+</code>
+</td>
+<td>
+Thing
+Description
+of
+a
+<a href= "#dfn-wot-thing-description-directory" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-wot-thing-description-directory-24">
+Thing
+Description
+Directory
+</a>
+</td>
+<td>
+<a href="#introduction-did-sec" data-matched-text= "[[[#introduction-did-sec]]]" class="sec-ref">
+<bdi class= "secno">
+6.5
+</bdi>
+DID
+Documents
+</a>
+</td>
+</tr>
+</tbody>
+</table>
+</section>
+</section>
+<section id="tdd-extensions-jsonschema" class="appendix">
+<div class="header-wrapper">
+<h2 id="a-json-schema-for-wot-discovery-td-extensions">
+<bdi class= "secno">
+A.
+</bdi>
+JSON
+Schema
+for
+WoT
+Discovery
+TD-extensions
+</h2>
+<a class="self-link" href="#tdd-extensions-jsonschema" aria-label= "Permalink for Appendix A.">
+</a>
+</div>
+The
+following
+JSON
+Schema
+specifies
+the
+extensions
+used
+in
+<a href= "#dfn-wot-enriched-thing-description" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-wot-enriched-thing-description-7">
+Enriched
+TDs
+</a>.
+It
+can
+be
+used
+for
+validating
+<a href="#dfn-td" class="internalDFN" data-link-type="dfn" id="ref-for-dfn-td-47">
+TDs
+</a>
+by
+a
+<a href= "#dfn-wot-tdd" class="internalDFN" data-link-type="dfn" id= "ref-for-dfn-wot-tdd-1">
+TDD
+</a>
+as
+prescribed
+in
+<a href= "#exploration-directory-api-things-validation" data-matched-text= "[[[#exploration-directory-api-things-validation]]]" class= "sec-ref">
+<bdi class="secno">
+7.3.2.1.6
+</bdi>
+Validation
+</a>.
+<pre class="advisement" aria-busy="false"><code class="hljs json">{
+  <span class="hljs-attr">"title"</span>: <span class=
+"hljs-string">"WoT Discovery TD-extensions Schema - 21 May 2021"</span>,
+  <span class="hljs-attr">"description"</span>: <span class=
+"hljs-string">"JSON Schema for validating TD instances with WoT Discovery extensions"</span>,
+  <span class="hljs-attr">"$schema "</span>: <span class=
+"hljs-string">"https://json-schema.org/draft/2019-09/schema#"</span>,
+  <span class="hljs-attr">"type"</span>: <span class=
+"hljs-string">"object"</span>,
+  <span class="hljs-attr">"properties"</span>: {
+    <span class="hljs-attr">"registration"</span>: {
+      <span class="hljs-attr">"type"</span>: <span class=
+"hljs-string">"object"</span>,
+      <span class="hljs-attr">"properties"</span>: {
+        <span class="hljs-attr">"created"</span>: {
+          <span class="hljs-attr">"type"</span>: <span class=
+"hljs-string">"string"</span>,
+          <span class="hljs-attr">"format"</span>: <span class=
+"hljs-string">"date-time"</span>
+        },
+        <span class="hljs-attr">"expires"</span>: {
+          <span class="hljs-attr">"type"</span>: <span class=
+"hljs-string">"string"</span>,
+          <span class="hljs-attr">"format"</span>: <span class=
+"hljs-string">"date-time"</span>
+        },
+        <span class="hljs-attr">"retrieved"</span>: {
+          <span class="hljs-attr">"type"</span>: <span class=
+"hljs-string">"string"</span>,
+          <span class="hljs-attr">"format"</span>: <span class=
+"hljs-string">"date-time"</span>
+        },
+        <span class="hljs-attr">"modified"</span>: {
+          <span class="hljs-attr">"type"</span>: <span class=
+"hljs-string">"string"</span>,
+          <span class="hljs-attr">"format"</span>: <span class=
+"hljs-string">"date-time"</span>
+        },
+        <span class="hljs-attr">"ttl"</span>: {
+          <span class="hljs-attr">"type"</span>: <span class=
+"hljs-string">"number"</span>
+        }
+      }
+    }
+  }
+}
+</code>
+</pre>
+</section>
+<section id="changes" class="appendix">
+<div class="header-wrapper">
+<h2 id="b-recent-specification-changes">
+<bdi class="secno">
+B.
+</bdi>
+Recent
+Specification
+Changes
+</h2>
+<a class="self-link" href="#changes" aria-label= "Permalink for Appendix B.">
+</a>
+</div>
+<section id="changes-from-11-july-2023-proposed-recommendation">
+<div class="header-wrapper">
+<h3 id="changes-from-pr">
+<bdi class="secno">
+B.1
+</bdi>
+Changes
+from
+11
+July
+2023
+Proposed
+Recommendation
+</h3>
+<a class="self-link" href="#changes-from-pr" aria-label= "Permalink for Appendix B.1">
+</a>
+</div>
+<ul>
+<li>
+No
+normative
+changes
+from
+Proposed
+Recommendation.
+</li>
+<li>
+Add
+errata
+link.
+</li>
+<li>
+Update
+process
+link
+to
+3
+November
+2023.
+</li>
+<li>
+Remove
+Editors'
+notes
+regarding
+date-time
+and
+Search
+API
+overview.
+</li>
+<li>
+Update
+references
+to
+DID
+registry
+and
+other
+WoT
+documents.
+</li>
+<li>
+<a href= "https://services.w3.org/htmldiff?doc1=https%3A%2F%2Fwww.w3.org%2FTR%2F2023%2FPR-wot-discovery-20230711%2F&amp;doc2=https%3A%2F%2Fraw.githubusercontent.com%2Fw3c%2Fwot-discovery%2Fmain%2Fpublication%2F6-rec%2FOverview.html">
+HTML
+Diff
+</a>
+</li>
+</ul>
+</section>
+<section id= "changes-from-19-january-2023-candidate-recommendation">
+<div class="header-wrapper">
+<h3 id="changes-from-cr">
+<bdi class="secno">
+B.2
+</bdi>
+Changes
+from
+19
+January
+2023
+Candidate
+Recommendation
+</h3>
+<a class="self-link" href="#changes-from-cr" aria-label= "Permalink for Appendix B.2">
+</a>
+</div>
+<ul>
+<li>
+No
+normative
+changes
+from
+Candidate
+Recommendation.
+</li>
+<li>
+Add
+reference
+to
+IoT'16
+paper
+by
+Arne
+Broering,
+Soumya
+Kanti
+Datta,
+and
+Christian
+Bonnet.
+</li>
+<li>
+At-risk
+assertions
+that
+did
+not
+receive
+sufficient
+implementations
+were
+removed
+or
+converted
+to
+informative
+statements.
+</li>
+<li>
+<a href= "https://services.w3.org/htmldiff?doc1=https%3A%2F%2Fwww.w3.org%2FTR%2F2023%2FCR-wot-discovery-20230119%2F&amp;doc2=https%3A%2F%2Fraw.githubusercontent.com%2Fw3c%2Fwot-discovery%2Fpr-candidate%2Fstatic.html">
+HTML
+Diff
+</a>
+</li>
+</ul>
+</section>
+<section id="changes-from-10-august-2022-working-draft">
+<div class="header-wrapper">
+<h3 id="changes-from-third-draft">
+<bdi class="secno">
+B.3
+</bdi>
+Changes
+from
+10
+August
+2022
+Working
+Draft
+</h3>
+<a class="self-link" href="#changes-from-third-draft" aria-label= "Permalink for Appendix B.3">
+</a>
+</div>
+<ul>
+<li>
+Define
+sorting
+order
+to
+be
+based
+on
+Unicode
+code
+points.
+</li>
+<li>
+Clarify
+3x
+rule
+for
+DDoS
+migitation
+to
+allow
+padding
+in
+request,
+and
+require
+it
+only
+outside
+of
+protected
+local
+networks.
+</li>
+<li>
+Define
+content
+types
+to
+be
+used
+for
+CoAP
+servers,
+paralleling
+TD
+servers.
+</li>
+<li>
+Update
+DID
+service
+names
+and
+refine
+DID
+assertions
+and
+add
+examples
+to
+clarify
+use
+for
+Introductions.
+</li>
+<li>
+Update
+DNS-SD
+section
+to
+include
+explicit
+scheme
+in
+TXT
+field.
+</li>
+<li>
+Replace
+reference
+to
+draft
+CoRE-RD
+with
+final
+specification
+published
+as
+RFC9176.
+</li>
+</ul>
+</section>
+<section id="changes-from-2-june-2021-working-draft">
+<div class="header-wrapper">
+<h3 id="changes-from-second-draft">
+<bdi class="secno">
+B.4
+</bdi>
+Changes
+from
+2
+June
+2021
+Working
+Draft
+</h3>
+<a class="self-link" href="#changes-from-second-draft" aria-label= "Permalink for Appendix B.4">
+</a>
+</div>
+<ul>
+<li>
+Use
+<code>
+wot
+</code>
+for
+well-known
+URI
+service
+name.
+</li>
+<li>
+Refer
+to
+TD
+and
+Architecture
+specs
+for
+general
+constraints
+on
+secure
+transport.
+</li>
+<li>
+Define
+requirements
+for
+CoAP-based
+TD
+Servers.
+</li>
+<li>
+Introduction
+of
+TD
+Server
+exploration,
+with
+self-description
+as
+a
+special
+case.
+</li>
+<li>
+Elaboration
+of
+class
+diagram
+to
+clarify
+that
+not
+all
+Directories
+need
+to
+be
+self-describing.
+</li>
+<li>
+Clarify
+and
+consolidate
+error
+codes
+and
+ontology.
+</li>
+<li>
+Add
+assertions
+for
+UTF-8
+supporting
+internationalization.
+</li>
+<li>
+Update
+overview
+figure
+showing
+introduction
+and
+exploration
+mechanisms.
+</li>
+<li>
+Add
+Discoverer
+section
+defining
+requirements
+for
+discovery
+clients.
+</li>
+<li>
+Use
+Thing
+Model
+instead
+of
+a
+Thing
+Description
+example
+for
+Directory
+API.
+</li>
+<li>
+Refactor
+Directory
+Service
+API
+(td-&gt;thing,
+split
+anonymous
+create
+action,
+retrieve
+one
+and
+search
+as
+actions,
+listing
+as
+things
+property,
+split
+events)
+</li>
+<li>
+Add
+amplification
+DDOS
+security
+consideration.
+</li>
+<li>
+Split
+Security
+and
+Privacy
+Considerations
+into
+separate
+sections.
+</li>
+<li>
+Define
+status
+of
+search
+mechanisms:
+JSON
+Path,
+XPath,
+and
+SPARQL.
+</li>
+<li>
+Pagination
+as
+array
+and
+pagination
+as
+collection.
+</li>
+<li>
+Updates
+to
+events
+API.
+</li>
+<li>
+TD
+expiry
+management.
+</li>
+<li>
+HEAD
+method
+support.
+</li>
+</ul>
+</section>
+<section id= "changes-from-24-november-2020-first-public-working-draft">
+<div class="header-wrapper">
+<h3 id="changes-from-first-draft">
+<bdi class="secno">
+B.5
+</bdi>
+Changes
+from
+24
+November
+2020
+First
+Public
+Working
+Draft
+</h3>
+<a class="self-link" href="#changes-from-first-draft" aria-label= "Permalink for Appendix B.5">
+</a>
+</div>
+<ul>
+<li>
+Update
+name
+of
+directory
+service
+to
+"Thing
+Description
+Directory"
+with
+acronym
+TDD,
+to
+avoid
+confusion
+with
+the
+acronym
+TD
+used
+for
+Thing
+Descriptions.
+</li>
+<li>
+Elaboration
+of
+complete
+API
+for
+registration
+of
+a
+Thing
+Description
+with
+a
+Thing
+Description
+Directory,
+including
+support
+for
+creation,
+update,
+retrieval,
+deletion,
+and
+listing.
+</li>
+<li>
+Add
+recommendation
+that
+TDs
+be
+validated
+before
+storage
+in
+a
+directory.
+Note:
+this
+corresponds
+to
+work
+under
+way
+in
+the
+TD
+spec
+to
+precisely
+define
+appropriate
+levels
+of
+automatic
+validation
+for
+different
+contexts,
+including
+directory
+registration.
+</li>
+<li>
+Addition
+of
+Security
+and
+Privacy
+Considerations
+regarding
+Denial
+of
+Service
+and
+Location
+Tracking.
+</li>
+<li>
+Addition
+of
+IANA
+Considerations
+regarding
+CoRE
+Resource
+Types.
+</li>
+<li>
+Definition
+of
+Enriched
+TD
+to
+support
+embedded
+metadata
+in
+TDs
+returned
+by
+a
+TDD.
+</li>
+<li>
+Updates
+to
+description
+of
+exploration
+to
+avoid
+unnecessary
+dependence
+on
+HTTP
+(in
+the
+future,
+other
+protocols
+may
+be
+supported).
+</li>
+<li>
+Use
+of
+"resource
+type"
+instead
+of
+"endpoint
+type"
+when
+describing
+entry
+in
+CoRE
+RD.
+</li>
+<li>
+Addition
+of
+ontology
+for
+TDDs
+that
+include
+the
+type
+<code>
+DirectoryDescription
+</code>
+identifying
+TDs
+of
+directories
+and
+a
+type
+<code>
+LinkDescription
+</code>
+to
+identify
+a
+TD
+that
+is
+just
+a
+link
+to
+another
+TD
+(useful
+for
+referring
+to
+remote
+directories
+in
+order
+to
+support
+federation).
+</li>
+<li>
+Add
+section
+for
+self-description
+exploration
+mechanism.
+This
+supports
+the
+use
+case
+where
+a
+Thing
+hosts
+its
+own
+TD
+and
+peer-to-peer
+Thing
+communication.
+</li>
+<li>
+Addition
+of
+diagram
+showing
+the
+directory
+information
+model.
+</li>
+<li>
+Removal
+of
+reference
+to
+Issue
+16,
+citing
+CRUD
+interface
+requirements.
+Replaced
+with
+CRUDL
+(CRUD
++
+Listing)
+interface
+requirement.
+</li>
+<li>
+<em class="rfc2119">
+MAY
+</em>
+assertion
+added
+to
+explicitly
+permit
+implementation
+of
+SPARQL
+federation,
+and
+a
+requirement
+that
+if
+implemented,
+it
+needs
+to
+follow
+the
+SPARQL
+1.1
+specification.
+</li>
+<li>
+Updates
+to
+references:
+more
+recent
+versions
+of
+CoRE
+RD,
+DID
+Core,
+Eventsource,
+JSON-LD,
+and
+JSON
+Path
+specifications.
+Use
+of
+datatracker
+service
+(and
+URLs)
+to
+reference
+IETF
+RFCs.
+Addition
+of
+normative
+references
+to
+RFC7396
+and
+RFC7540.
+</li>
+</ul>
+</section>
+</section>
+<section id="acknowledgements" class="appendix normative">
+<div class="header-wrapper">
+<h2 id="c-acknowledgments">
+<bdi class="secno">
+C.
+</bdi>
+Acknowledgments
+</h2>
+<a class="self-link" href="#acknowledgements" aria-label= "Permalink for Appendix C.">
+</a>
+</div>
+<p>
+Special
+thanks
+to
+Arne
+Broering,
+Soumya
+Kanti
+Datta,
+and
+Christian
+Bonnet
+for
+their
+survey
+work
+on
+existing
+discovery
+mechannisms
+in
+IoT.
+Special
+thanks
+to
+Philipp
+Blum,
+Victor
+Charpeney,
+Ben
+Francis,
+Christian
+Glomb,
+Daniel
+Peintner,
+Christine
+Perey,
+Jan
+Romann,
+and
+Elodie
+Thieblin
+for
+their
+contributions
+to
+this
+document.
+</p>
+<p>
+Many
+thanks
+to
+the
+<abbr title= "World Wide Web Consortium">
+W3C
+</abbr>
+staff,
+especially
+Kazuyuki
+Ashimura
+and
+Dominique
+Hazael-Massieux,
+and
+all
+other
+active
+Participants
+of
+the
+<abbr title= "World Wide Web Consortium">
+W3C
+</abbr>
+Web
+of
+Things
+Interest
+Group
+(WoT
+IG)
+and
+Working
+Group
+(WoT
+WG)
+for
+their
+support,
+technical
+input
+and
+suggestions
+that
+led
+to
+improvements
+to
+this
+document.
+</p>
+</section>
+<section id="references" class="appendix">
+<div class="header-wrapper">
+<h2 id="d-references">
+<bdi class="secno">
+D.
+</bdi>
+References
+</h2>
+<a class="self-link" href="#references" aria-label= "Permalink for Appendix D.">
+</a>
+</div>
+<section id="normative-references">
+<div class="header-wrapper">
+<h3 id="d-1-normative-references">
+<bdi class="secno">
+D.1
+</bdi>
+Normative
+references
+</h3>
+<a class="self-link" href="#normative-references" aria-label= "Permalink for Appendix D.1">
+</a>
+</div>
+<dl class="bibliography">
+<dt id="bib-amplification-attacks">
+[AMPLIFICATION-ATTACKS]
+</dt>
+<dd>
+<a href= "https://datatracker.ietf.org/doc/html/draft-irtf-t2trg-amplification-attacks">
+<cite>
+Amplification
+Attacks
+Using
+the
+Constrained
+Application
+Protocol
+(CoAP)
+</cite>
+</a>.
+John
+Preuß
+Mattsson;
+Göran
+Selander;
+Christian
+Amsüss.
+IETF.
+DRAFT.
+URL:
+<a href= "https://datatracker.ietf.org/doc/html/draft-irtf-t2trg-amplification-attacks">
+https://datatracker.ietf.org/doc/html/draft-irtf-t2trg-amplification-attacks
+</a>
+</dd>
+<dt id="bib-did-core">
+[DID-CORE]
+</dt>
+<dd>
+<a href="https://www.w3.org/TR/did-core/">
+<cite>
+Decentralized
+Identifiers
+(DIDs)
+v1.0
+</cite>
+</a>.
+Manu
+Sporny;
+Amy
+Guy;
+Markus
+Sabadello;
+Drummond
+Reed.
+W3C.
+19
+July
+2022.
+W3C
+Recommendation.
+URL:
+<a href= "https://www.w3.org/TR/did-core/">
+https://www.w3.org/TR/did-core/
+</a>
+</dd>
+<dt id="bib-did-spec-registries">
+[did-spec-registries]
+</dt>
+<dd>
+<a href="https://www.w3.org/TR/did-spec-registries/">
+<cite>
+DID
+Specification
+Registries
+</cite>
+</a>.
+Orie
+Steele;
+Manu
+Sporny.
+W3C.
+11
+September
+2023.
+W3C
+Working
+Group
+Note.
+URL:
+<a href= "https://www.w3.org/TR/did-spec-registries/">
+https://www.w3.org/TR/did-spec-registries/
+</a>
+</dd>
+<dt id="bib-discovery-categorization-iot">
+[Discovery-Categorization-IoT]
+</dt>
+<dd>
+<a href= "https://dl.acm.org/doi/10.1145/2991561.2991570">
+<cite>
+A
+Categorization
+of
+Discovery
+Technologies
+for
+the
+Internet
+of
+Things
+</cite>
+</a>.
+Arne
+Broering;
+Soumya
+Kanti
+Datta;
+Christian
+Bonnet.
+Association
+of
+Computing
+Machinery
+(ACM):
+IoT'16
+Proceedings.
+7-9
+November
+2016.
+URL:
+<a href= "https://dl.acm.org/doi/10.1145/2991561.2991570">
+https://dl.acm.org/doi/10.1145/2991561.2991570
+</a>
+</dd>
+<dt id="bib-gdpr-defs">
+[GDPR-Defs]
+</dt>
+<dd>
+<a href="https://gdpr-info.eu/art-4-gdpr/">
+<cite>
+General
+Data
+Protection
+Regulation
+(GDPR)
+Article
+4
+-
+Definitions
+</cite>
+</a>.
+European
+Union
+(EU)
+and
+the
+European
+Economic
+Area
+(EEA).
+URL:
+<a href= "https://gdpr-info.eu/art-4-gdpr/">
+https://gdpr-info.eu/art-4-gdpr/
+</a>
+</dd>
+<dt id="bib-html">
+[HTML]
+</dt>
+<dd>
+<a href="https://html.spec.whatwg.org/multipage/">
+<cite>
+HTML
+Standard
+</cite>
+</a>.
+Anne
+van
+Kesteren;
+Domenic
+Denicola;
+Ian
+Hickson;
+Philip
+Jägenstedt;
+Simon
+Pieters.
+WHATWG.
+Living
+Standard.
+URL:
+<a href= "https://html.spec.whatwg.org/multipage/">
+https://html.spec.whatwg.org/multipage/
+</a>
+</dd>
+<dt id="bib-json-ld11">
+[JSON-LD11]
+</dt>
+<dd>
+<a href="https://www.w3.org/TR/json-ld11/">
+<cite>
+JSON-LD
+1.1
+</cite>
+</a>.
+Gregg
+Kellogg;
+Pierre-Antoine
+Champin;
+Dave
+Longley.
+W3C.
+16
+July
+2020.
+W3C
+Recommendation.
+URL:
+<a href= "https://www.w3.org/TR/json-ld11/">
+https://www.w3.org/TR/json-ld11/
+</a>
+</dd>
+<dt id="bib-owasp-top-10">
+[OWASP-Top-10]
+</dt>
+<dd>
+<a href="https://owasp.org/www-project-top-ten/">
+<cite>
+OWASP
+Top
+Ten
+</cite>
+</a>.
+OWASP.
+URL:
+<a href= "https://owasp.org/www-project-top-ten/">
+https://owasp.org/www-project-top-ten/
+</a>
+</dd>
+<dt id="bib-rfc1738">
+[RFC1738]
+</dt>
+<dd>
+<a href="https://www.rfc-editor.org/rfc/rfc1738">
+<cite>
+Uniform
+Resource
+Locators
+(URL)
+</cite>
+</a>.
+T.
+Berners-Lee;
+L.
+Masinter;
+M.
+McCahill.
+IETF.
+December
+1994.
+Proposed
+Standard.
+URL:
+<a href= "https://www.rfc-editor.org/rfc/rfc1738">
+https://www.rfc-editor.org/rfc/rfc1738
+</a>
+</dd>
+<dt id="bib-rfc2119">
+[RFC2119]
+</dt>
+<dd>
+<a href="https://www.rfc-editor.org/rfc/rfc2119">
+<cite>
+Key
+words
+for
+use
+in
+RFCs
+to
+Indicate
+Requirement
+Levels
+</cite>
+</a>.
+S.
+Bradner.
+IETF.
+March
+1997.
+Best
+Current
+Practice.
+URL:
+<a href= "https://www.rfc-editor.org/rfc/rfc2119">
+https://www.rfc-editor.org/rfc/rfc2119
+</a>
+</dd>
+<dt id="bib-rfc3339">
+[RFC3339]
+</dt>
+<dd>
+<a href="https://www.rfc-editor.org/rfc/rfc3339">
+<cite>
+Date
+and
+Time
+on
+the
+Internet:
+Timestamps
+</cite>
+</a>.
+G.
+Klyne;
+C.
+Newman.
+IETF.
+July
+2002.
+Proposed
+Standard.
+URL:
+<a href= "https://www.rfc-editor.org/rfc/rfc3339">
+https://www.rfc-editor.org/rfc/rfc3339
+</a>
+</dd>
+<dt id="bib-rfc4122">
+[RFC4122]
+</dt>
+<dd>
+<a href="https://www.rfc-editor.org/rfc/rfc4122">
+<cite>
+A
+Universally
+Unique
+IDentifier
+(UUID)
+URN
+Namespace
+</cite>
+</a>.
+P.
+Leach;
+M.
+Mealling;
+R.
+Salz.
+IETF.
+July
+2005.
+Proposed
+Standard.
+URL:
+<a href= "https://www.rfc-editor.org/rfc/rfc4122">
+https://www.rfc-editor.org/rfc/rfc4122
+</a>
+</dd>
+<dt id="bib-rfc4279">
+[RFC4279]
+</dt>
+<dd>
+<a href= "https://www.rfc-editor.org/rfc/rfc4279">
+<cite>
+Pre-Shared
+Key
+Ciphersuites
+for
+Transport
+Layer
+Security
+(TLS)
+</cite>
+</a>.
+P.
+Eronen,
+Ed.;
+H.
+Tschofenig,
+Ed..
+IETF.
+December
+2005.
+Proposed
+Standard.
+URL:
+<a href= "https://www.rfc-editor.org/rfc/rfc4279">
+https://www.rfc-editor.org/rfc/rfc4279
+</a>
+</dd>
+<dt id="bib-rfc6335">
+[RFC6335]
+</dt>
+<dd>
+<a href="https://www.rfc-editor.org/rfc/rfc6335">
+<cite>
+Internet
+Assigned
+Numbers
+Authority
+(IANA)
+Procedures
+for
+the
+Management
+of
+the
+Service
+Name
+and
+Transport
+Protocol
+Port
+Number
+Registry
+</cite>
+</a>.
+M.
+Cotton;
+L.
+Eggert;
+J.
+Touch;
+M.
+Westerlund;
+S.
+Cheshire.
+IETF.
+August
+2011.
+Best
+Current
+Practice.
+URL:
+<a href="https://www.rfc-editor.org/rfc/rfc6335">
+https://www.rfc-editor.org/rfc/rfc6335
+</a>
+</dd>
+<dt id="bib-rfc6690">
+[RFC6690]
+</dt>
+<dd>
+<a href= "https://www.rfc-editor.org/rfc/rfc6690">
+<cite>
+Constrained
+RESTful
+Environments
+(CoRE)
+Link
+Format
+</cite>
+</a>.
+Z.
+Shelby.
+IETF.
+August
+2012.
+Proposed
+Standard.
+URL:
+<a href= "https://www.rfc-editor.org/rfc/rfc6690">
+https://www.rfc-editor.org/rfc/rfc6690
+</a>
+</dd>
+<dt id="bib-rfc6762">
+[RFC6762]
+</dt>
+<dd>
+<a href= "https://www.rfc-editor.org/rfc/rfc6762">
+<cite>
+Multicast
+DNS
+</cite>
+</a>.
+S.
+Cheshire;
+M.
+Krochmal.
+IETF.
+February
+2013.
+Proposed
+Standard.
+URL:
+<a href= "https://www.rfc-editor.org/rfc/rfc6762">
+https://www.rfc-editor.org/rfc/rfc6762
+</a>
+</dd>
+<dt id="bib-rfc6763">
+[RFC6763]
+</dt>
+<dd>
+<a href= "https://www.rfc-editor.org/rfc/rfc6763">
+<cite>
+DNS-Based
+Service
+Discovery
+</cite>
+</a>.
+S.
+Cheshire;
+M.
+Krochmal.
+IETF.
+February
+2013.
+Proposed
+Standard.
+URL:
+<a href= "https://www.rfc-editor.org/rfc/rfc6763">
+https://www.rfc-editor.org/rfc/rfc6763
+</a>
+</dd>
+<dt id="bib-rfc7231">
+[RFC7231]
+</dt>
+<dd>
+<a href="https://httpwg.org/specs/rfc7231.html">
+<cite>
+Hypertext
+Transfer
+Protocol
+(HTTP/1.1):
+Semantics
+and
+Content
+</cite>
+</a>.
+R.
+Fielding,
+Ed.;
+J.
+Reschke,
+Ed..
+IETF.
+June
+2014.
+Proposed
+Standard.
+URL:
+<a href= "https://httpwg.org/specs/rfc7231.html">
+https://httpwg.org/specs/rfc7231.html
+</a>
+</dd>
+<dt id="bib-rfc7396">
+[RFC7396]
+</dt>
+<dd>
+<a href="https://www.rfc-editor.org/rfc/rfc7396">
+<cite>
+JSON
+Merge
+Patch
+</cite>
+</a>.
+P.
+Hoffman;
+J.
+Snell.
+IETF.
+October
+2014.
+Proposed
+Standard.
+URL:
+<a href= "https://www.rfc-editor.org/rfc/rfc7396">
+https://www.rfc-editor.org/rfc/rfc7396
+</a>
+</dd>
+<dt id="bib-rfc7595">
+[RFC7595]
+</dt>
+<dd>
+<a href= "https://www.rfc-editor.org/rfc/rfc7595">
+<cite>
+Guidelines
+and
+Registration
+Procedures
+for
+URI
+Schemes
+</cite>
+</a>.
+D.
+Thaler,
+Ed.;
+T.
+Hansen;
+T.
+Hardie.
+IETF.
+June
+2015.
+Best
+Current
+Practice.
+URL:
+<a href= "https://www.rfc-editor.org/rfc/rfc7595">
+https://www.rfc-editor.org/rfc/rfc7595
+</a>
+</dd>
+<dt id="bib-rfc7807">
+[RFC7807]
+</dt>
+<dd>
+<a href="https://www.rfc-editor.org/rfc/rfc7807">
+<cite>
+Problem
+Details
+for
+HTTP
+APIs
+</cite>
+</a>.
+M.
+Nottingham;
+E.
+Wilde.
+IETF.
+March
+2016.
+Proposed
+Standard.
+URL:
+<a href= "https://www.rfc-editor.org/rfc/rfc7807">
+https://www.rfc-editor.org/rfc/rfc7807
+</a>
+</dd>
+<dt id="bib-rfc7959">
+[RFC7959]
+</dt>
+<dd>
+<a href= "https://www.rfc-editor.org/rfc/rfc7959">
+<cite>
+Block-Wise
+Transfers
+in
+the
+Constrained
+Application
+Protocol
+(CoAP)
+</cite>
+</a>.
+C.
+Bormann;
+Z.
+Shelby,
+Ed..
+IETF.
+August
+2016.
+Proposed
+Standard.
+URL:
+<a href= "https://www.rfc-editor.org/rfc/rfc7959">
+https://www.rfc-editor.org/rfc/rfc7959
+</a>
+</dd>
+<dt id="bib-rfc8174">
+[RFC8174]
+</dt>
+<dd>
+<a href= "https://www.rfc-editor.org/rfc/rfc8174">
+<cite>
+Ambiguity
+of
+Uppercase
+vs
+Lowercase
+in
+RFC
+2119
+Key
+Words
+</cite>
+</a>.
+B.
+Leiba.
+IETF.
+May
+2017.
+Best
+Current
+Practice.
+URL:
+<a href= "https://www.rfc-editor.org/rfc/rfc8174">
+https://www.rfc-editor.org/rfc/rfc8174
+</a>
+</dd>
+<dt id="bib-rfc8288">
+[RFC8288]
+</dt>
+<dd>
+<a href="https://httpwg.org/specs/rfc8288.html">
+<cite>
+Web
+Linking
+</cite>
+</a>.
+M.
+Nottingham.
+IETF.
+October
+2017.
+Proposed
+Standard.
+URL:
+<a href= "https://httpwg.org/specs/rfc8288.html">
+https://httpwg.org/specs/rfc8288.html
+</a>
+</dd>
+<dt id="bib-rfc8615">
+[RFC8615]
+</dt>
+<dd>
+<a href= "https://www.rfc-editor.org/rfc/rfc8615">
+<cite>
+Well-Known
+Uniform
+Resource
+Identifiers
+(URIs)
+</cite>
+</a>.
+M.
+Nottingham.
+IETF.
+May
+2019.
+Proposed
+Standard.
+URL:
+<a href= "https://www.rfc-editor.org/rfc/rfc8615">
+https://www.rfc-editor.org/rfc/rfc8615
+</a>
+</dd>
+<dt id="bib-rfc8981">
+[RFC8981]
+</dt>
+<dd>
+<a href= "https://www.rfc-editor.org/rfc/rfc8981">
+<cite>
+Temporary
+Address
+Extensions
+for
+Stateless
+Address
+Autoconfiguration
+in
+IPv6
+</cite>
+</a>.
+F.
+Gont;
+S.
+Krishnan;
+T.
+Narten;
+R.
+Draves.
+IETF.
+February
+2021.
+Proposed
+Standard.
+URL:
+<a href= "https://www.rfc-editor.org/rfc/rfc8981">
+https://www.rfc-editor.org/rfc/rfc8981
+</a>
+</dd>
+<dt id="bib-rfc9000">
+[RFC9000]
+</dt>
+<dd>
+<a href="https://www.rfc-editor.org/rfc/rfc9000">
+<cite>
+QUIC:
+A
+UDP-Based
+Multiplexed
+and
+Secure
+Transport
+</cite>
+</a>.
+J.
+Iyengar,
+Ed.;
+M.
+Thomson,
+Ed..
+IETF.
+May
+2021.
+Proposed
+Standard.
+URL:
+<a href= "https://www.rfc-editor.org/rfc/rfc9000">
+https://www.rfc-editor.org/rfc/rfc9000
+</a>
+</dd>
+<dt id="bib-rfc9176">
+[RFC9176]
+</dt>
+<dd>
+<a href= "https://www.rfc-editor.org/rfc/rfc9176">
+<cite>
+Constrained
+RESTful
+Environments
+(CoRE)
+Resource
+Directory
+</cite>
+</a>.
+C.
+Amsüss,
+Ed.;
+Z.
+Shelby;
+M.
+Koster;
+C.
+Bormann;
+P.
+van
+der
+Stok.
+IETF.
+April
+2022.
+Proposed
+Standard.
+URL:
+<a href= "https://www.rfc-editor.org/rfc/rfc9176">
+https://www.rfc-editor.org/rfc/rfc9176
+</a>
+</dd>
+<dt id="bib-sparql11-overview">
+[SPARQL11-OVERVIEW]
+</dt>
+<dd>
+<a href="https://www.w3.org/TR/sparql11-overview/">
+<cite>
+SPARQL
+1.1
+Overview
+</cite>
+</a>.
+The
+W3C
+SPARQL
+Working
+Group.
+W3C.
+21
+March
+2013.
+W3C
+Recommendation.
+URL:
+<a href= "https://www.w3.org/TR/sparql11-overview/">
+https://www.w3.org/TR/sparql11-overview/
+</a>
+</dd>
+<dt id="bib-wot-architecture11">
+[wot-architecture11]
+</dt>
+<dd>
+<a href="https://www.w3.org/TR/wot-architecture11/">
+<cite>
+Web
+of
+Things
+(WoT)
+Architecture
+1.1
+</cite>
+</a>.
+Michael
+Lagally;
+Ryuichi
+Matsukura;
+Kunihiko
+Toumura;
+Michael
+McCool.
+W3C.
+<del class="diff-old">30
+November
+</del>
+<ins class="diff-chg">5
+December
+</ins>
+2023.
+W3C
+Proposed
+Recommendation.
+URL:
+<a href= "https://www.w3.org/TR/wot-architecture11/">
+https://www.w3.org/TR/wot-architecture11/
+</a>
+</dd>
+<dt id="bib-wot-thing-description11">
+[wot-thing-description11]
+</dt>
+<dd>
+<a href= "https://www.w3.org/TR/wot-thing-description11/">
+<cite>
+Web
+of
+Things
+(WoT)
+Thing
+Description
+1.1
+</cite>
+</a>.
+Sebastian
+Käbisch;
+Michael
+McCool;
+Ege
+Korkan.
+W3C.
+<del class="diff-old">30
+November
+</del>
+<ins class="diff-chg">5
+December
+</ins>
+2023.
+W3C
+Proposed
+Recommendation.
+URL:
+<a href= "https://www.w3.org/TR/wot-thing-description11/">
+https://www.w3.org/TR/wot-thing-description11/
+</a>
+</dd>
+<dt id="bib-wot-usecases">
+[wot-usecases]
+</dt>
+<dd>
+<a href="https://w3c.github.io/wot-usecases/">
+<cite>
+Web
+of
+Things
+(WoT):
+Use
+Cases
+</cite>
+</a>.
+Michael
+Lagally;
+Michael
+McCool;
+Ryuichi
+Matsukura;
+Tomoaki
+Mizushima.
+W3C.
+15
+October
+2020.
+Editor's
+Draft.
+URL:
+<a href= "https://w3c.github.io/wot-usecases/">
+https://w3c.github.io/wot-usecases/
+</a>
+</dd>
+<dt id="bib-xpath-31">
+[xpath-31]
+</dt>
+<dd>
+<a href="https://www.w3.org/TR/xpath-31/">
+<cite>
+XML
+Path
+Language
+(XPath)
+3.1
+</cite>
+</a>.
+Jonathan
+Robie;
+Michael
+Dyck;
+Josh
+Spiegel.
+W3C.
+21
+March
+2017.
+W3C
+Recommendation.
+URL:
+<a href= "https://www.w3.org/TR/xpath-31/">
+https://www.w3.org/TR/xpath-31/
+</a>
+</dd>
+</dl>
+</section>
+<section id="informative-references">
+<div class="header-wrapper">
+<h3 id="d-2-informative-references">
+<bdi class="secno">
+D.2
+</bdi>
+Informative
+references
+</h3>
+<a class="self-link" href="#informative-references" aria-label= "Permalink for Appendix D.2">
+</a>
+</div>
+<dl class="bibliography">
+<dt id="bib-jsonpath">
+[JSONPATH]
+</dt>
+<dd>
+<a href= "https://datatracker.ietf.org/doc/html/draft-ietf-jsonpath-base">
+<cite>
+JSONPath:
+Query
+expressions
+for
+JSON
+</cite>
+</a>.
+Stefan
+Gössner;
+Glyn
+Normington;
+Carsten
+Bormann.
+IETF.
+DRAFT.
+URL:
+<a href= "https://datatracker.ietf.org/doc/html/draft-ietf-jsonpath-base">
+https://datatracker.ietf.org/doc/html/draft-ietf-jsonpath-base
+</a>
+</dd>
+<dt id="bib-ldp-paging">
+[LDP-Paging]
+</dt>
+<dd>
+<a href="https://www.w3.org/TR/ldp-paging/">
+<cite>
+Linked
+Data
+Platform
+Paging
+1.0
+</cite>
+</a>.
+Steve
+Speicher;
+John
+Arwe;
+Ashok
+Malhotra.
+W3C.
+30
+June
+2015.
+W3C
+Working
+Group
+Note.
+URL:
+<a href= "https://www.w3.org/TR/ldp-paging/">
+https://www.w3.org/TR/ldp-paging/
+</a>
+</dd>
+<dt id="bib-rest-iot">
+[REST-IOT]
+</dt>
+<dd>
+<a href= "https://datatracker.ietf.org/doc/html/draft-irtf-t2trg-rest-iot-06">
+<cite>
+RESTful
+Design
+for
+Internet
+of
+Things
+Systems
+</cite>
+</a>.
+Ari
+Keranen;
+Matthias
+Kovatsch;
+Klaus
+Hartke.
+IETF.
+11
+May
+2020.
+URL:
+<a href= "https://datatracker.ietf.org/doc/html/draft-irtf-t2trg-rest-iot-06">
+https://datatracker.ietf.org/doc/html/draft-irtf-t2trg-rest-iot-06
+</a>
+</dd>
+<dt id="bib-rfc7230">
+[RFC7230]
+</dt>
+<dd>
+<a href="https://httpwg.org/specs/rfc7230.html">
+<cite>
+Hypertext
+Transfer
+Protocol
+(HTTP/1.1):
+Message
+Syntax
+and
+Routing
+</cite>
+</a>.
+R.
+Fielding,
+Ed.;
+J.
+Reschke,
+Ed..
+IETF.
+June
+2014.
+Proposed
+Standard.
+URL:
+<a href= "https://httpwg.org/specs/rfc7230.html">
+https://httpwg.org/specs/rfc7230.html
+</a>
+</dd>
+<dt id="bib-rfc7540">
+[RFC7540]
+</dt>
+<dd>
+<a href="https://httpwg.org/specs/rfc7540.html">
+<cite>
+Hypertext
+Transfer
+Protocol
+Version
+2
+(HTTP/2)
+</cite>
+</a>.
+M.
+Belshe;
+R.
+Peon;
+M.
+Thomson,
+Ed..
+IETF.
+May
+2015.
+Proposed
+Standard.
+URL:
+<a href= "https://httpwg.org/specs/rfc7540.html">
+https://httpwg.org/specs/rfc7540.html
+</a>
+</dd>
+<dt id="bib-rfc8323">
+[RFC8323]
+</dt>
+<dd>
+<a href="https://www.rfc-editor.org/rfc/rfc8323">
+<cite>
+CoAP
+(Constrained
+Application
+Protocol)
+over
+TCP,
+TLS,
+and
+WebSockets
+</cite>
+</a>.
+C.
+Bormann;
+S.
+Lemay;
+H.
+Tschofenig;
+K.
+Hartke;
+B.
+Silverajan;
+B.
+Raymor,
+Ed..
+IETF.
+February
+2018.
+Proposed
+Standard.
+URL:
+<a href= "https://www.rfc-editor.org/rfc/rfc8323">
+https://www.rfc-editor.org/rfc/rfc8323
+</a>
+</dd>
+<dt id="bib-wot-security">
+[WOT-SECURITY]
+</dt>
+<dd>
+<a href="https://www.w3.org/TR/wot-security/">
+<cite>
+Web
+of
+Things
+(WoT)
+Security
+and
+Privacy
+Guidelines
+</cite>
+</a>.
+Elena
+Reshetova;
+Michael
+McCool.
+W3C.
+6
+November
+2019.
+W3C
+Working
+Group
+Note.
+URL:
+<a href= "https://www.w3.org/TR/wot-security/">
+https://www.w3.org/TR/wot-security/
+</a>
+</dd>
+</dl>
+</section>
+</section>
+<p role="navigation" id="back-to-top">
+<a href="#title">
+<abbr title= "Back to Top">
+↑
+</abbr>
+</a>
+</p>
+<div class="dfn-panel" hidden="" role="dialog" aria-modal="true" id="dfn-panel-for-dfn-thing" aria-label= "Links in this document to definition: Thing">
+<div>
+<a class="self-link" href="#dfn-thing" aria-label= "Permalink for definition: Thing. Activate to close this dialog.">
+Permalink
+</a>
+</div>
+<p>
+<b>
+Referenced
+in:
+</b>
+</p>
+<ul>
+<li>
+<a href="#ref-for-dfn-thing-1" title= "§ 6.4 CoRE Link Format and CoRE Resource Directory">
+§
+6.4
+CoRE
+Link
+Format
+and
+CoRE
+Resource
+Directory
+</a>
+</li>
+<li>
+<a href="#ref-for-dfn-thing-2" title="§ 6.5 DID Documents">
+§
+6.5
+DID
+Documents
+</a>
+<a href="#ref-for-dfn-thing-3" title= "Reference 2">
+(2)
+</a>
+<a href="#ref-for-dfn-thing-4" title= "Reference 3">
+(3)
+</a>
+</li>
+<li>
+<a href="#ref-for-dfn-thing-5" title= "§ 7.2 Thing Description Server">
+§
+7.2
+Thing
+Description
+Server
+</a>
+</li>
+<li>
+<a href="#ref-for-dfn-thing-6" title= "§ 7.3 Thing Description Directory">
+§
+7.3
+Thing
+Description
+Directory
+</a>
+</li>
+<li>
+<a href="#ref-for-dfn-thing-7" title="§ 7.3.2.1.1 Creation">
+§
+7.3.2.1.1
+Creation
+</a>
+<a href="#ref-for-dfn-thing-8" title= "Reference 2">
+(2)
+</a>
+</li>
+</ul>
+</div>
+<div class="dfn-panel" hidden="" role="dialog" aria-modal="true" id="dfn-panel-for-dfn-thing-description" aria-label= "Links in this document to definition: Thing Description">
+<div>
+<a class="self-link" href="#dfn-thing-description" aria-label= "Permalink for definition: Thing Description. Activate to close this dialog.">
+Permalink
+</a>
+</div>
+<p>
+<b>
+Referenced
+in:
+</b>
+</p>
+<ul>
+<li>
+<a href="#ref-for-dfn-thing-description-1" title= "§ 4. Architecture">
+§
+4.
+Architecture
+</a>
+</li>
+</ul>
+</div>
+<div class="dfn-panel" hidden="" role="dialog" aria-modal="true" id="dfn-panel-for-dfn-td" aria-label= "Links in this document to definition: TD">
+<div>
+<a class="self-link" href="#dfn-td" aria-label= "Permalink for definition: TD. Activate to close this dialog.">
+Permalink
+</a>
+</div>
+<p>
+<b>
+Referenced
+in:
+</b>
+</p>
+<ul>
+<li>
+<a href="#ref-for-dfn-td-1" title="§ 6.5 DID Documents">
+§
+6.5
+DID
+Documents
+</a>
+<a href="#ref-for-dfn-td-2" title= "Reference 2">
+(2)
+</a>
+<a href="#ref-for-dfn-td-3" title= "Reference 3">
+(3)
+</a>
+</li>
+<li>
+<a href="#ref-for-dfn-td-4" title="§ 7.1 Overview">
+§
+7.1
+Overview
+</a>
+<a href="#ref-for-dfn-td-5" title= "Reference 2">
+(2)
+</a>
+</li>
+<li>
+<a href="#ref-for-dfn-td-6" title="§ 7.1.1.2 ThingLink">
+§
+7.1.1.2
+ThingLink
+</a>
+<a href="#ref-for-dfn-td-7" title= "Reference 2">
+(2)
+</a>
+<a href="#ref-for-dfn-td-8" title= "Reference 3">
+(3)
+</a>
+</li>
+<li>
+<a href="#ref-for-dfn-td-9" title= "§ 7.2 Thing Description Server">
+§
+7.2
+Thing
+Description
+Server
+</a>
+<a href="#ref-for-dfn-td-10" title="Reference 2">
+(2)
+</a>
+<a href= "#ref-for-dfn-td-11" title="Reference 3">
+(3)
+</a>
+<a href= "#ref-for-dfn-td-12" title="Reference 4">
+(4)
+</a>
+<a href= "#ref-for-dfn-td-13" title="Reference 5">
+(5)
+</a>
+<a href= "#ref-for-dfn-td-14" title="Reference 6">
+(6)
+</a>
+<a href= "#ref-for-dfn-td-15" title="Reference 7">
+(7)
+</a>
+<a href= "#ref-for-dfn-td-16" title="Reference 8">
+(8)
+</a>
+<a href= "#ref-for-dfn-td-17" title="Reference 9">
+(9)
+</a>
+<a href= "#ref-for-dfn-td-18" title="Reference 10">
+(10)
+</a>
+<a href= "#ref-for-dfn-td-19" title="Reference 11">
+(11)
+</a>
+<a href= "#ref-for-dfn-td-20" title="Reference 12">
+(12)
+</a>
+<a href= "#ref-for-dfn-td-21" title="Reference 13">
+(13)
+</a>
+<a href= "#ref-for-dfn-td-22" title="Reference 14">
+(14)
+</a>
+<a href= "#ref-for-dfn-td-23" title="Reference 15">
+(15)
+</a>
+<a href= "#ref-for-dfn-td-24" title="Reference 16">
+(16)
+</a>
+<a href= "#ref-for-dfn-td-25" title="Reference 17">
+(17)
+</a>
+<a href= "#ref-for-dfn-td-26" title="Reference 18">
+(18)
+</a>
+<a href= "#ref-for-dfn-td-27" title="Reference 19">
+(19)
+</a>
+</li>
+<li>
+<a href="#ref-for-dfn-td-28" title= "§ 7.3.1 Information Model">
+§
+7.3.1
+Information
+Model
+</a>
+<a href= "#ref-for-dfn-td-29" title="Reference 2">
+(2)
+</a>
+</li>
+<li>
+<a href="#ref-for-dfn-td-30" title= "§ 7.3.1.1 Registration Information">
+§
+7.3.1.1
+Registration
+Information
+</a>
+<a href="#ref-for-dfn-td-31" title= "Reference 2">
+(2)
+</a>
+<a href="#ref-for-dfn-td-32" title= "Reference 3">
+(3)
+</a>
+<a href="#ref-for-dfn-td-33" title= "Reference 4">
+(4)
+</a>
+</li>
+<li>
+<a href="#ref-for-dfn-td-34" title= "§ 7.3.1.2 Registration Expiry">
+§
+7.3.1.2
+Registration
+Expiry
+</a>
+<a href="#ref-for-dfn-td-35" title="Reference 2">
+(2)
+</a>
+<a href= "#ref-for-dfn-td-36" title="Reference 3">
+(3)
+</a>
+<a href= "#ref-for-dfn-td-37" title="Reference 4">
+(4)
+</a>
+</li>
+<li>
+<a href="#ref-for-dfn-td-38" title="§ 7.3.2.1 Things API">
+§
+7.3.2.1
+Things
+API
+</a>
+<a href="#ref-for-dfn-td-39" title= "Reference 2">
+(2)
+</a>
+</li>
+<li>
+<a href="#ref-for-dfn-td-40" title="§ 7.3.2.1.1 Creation">
+§
+7.3.2.1.1
+Creation
+</a>
+<a href="#ref-for-dfn-td-41" title= "Reference 2">
+(2)
+</a>
+</li>
+<li>
+<a href="#ref-for-dfn-td-42" title="§ 7.3.2.1.3 Update">
+§
+7.3.2.1.3
+Update
+</a>
+</li>
+<li>
+<a href="#ref-for-dfn-td-43" title="§ 7.3.2.2 Events API">
+§
+7.3.2.2
+Events
+API
+</a>
+<a href="#ref-for-dfn-td-44" title= "Reference 2">
+(2)
+</a>
+</li>
+<li>
+<a href="#ref-for-dfn-td-45" title="§ 7.3.2.3 Search API">
+§
+7.3.2.3
+Search
+API
+</a>
+</li>
+<li>
+<a href="#ref-for-dfn-td-46" title= "§ 10.1 Incremental Transfer">
+§
+10.1
+Incremental
+Transfer
+</a>
+</li>
+<li>
+<a href="#ref-for-dfn-td-47" title= "§ A. JSON Schema for WoT Discovery TD-extensions">
+§
+A.
+JSON
+Schema
+for
+WoT
+Discovery
+TD-extensions
+</a>
+</li>
+</ul>
+</div>
+<div class="dfn-panel" hidden="" role="dialog" aria-modal="true" id="dfn-panel-for-dfn-thing-model" aria-label= "Links in this document to definition: Thing Model">
+<div>
+<a class="self-link" href="#dfn-thing-model" aria-label= "Permalink for definition: Thing Model. Activate to close this dialog.">
+Permalink
+</a>
+</div>
+<p>
+<b>
+Referenced
+in:
+</b>
+</p>
+<ul>
+<li>
+<a href="#ref-for-dfn-thing-model-1" title= "§ 7.3.2.4 API Specification (Thing Model)">
+§
+7.3.2.4
+API
+Specification
+(Thing
+Model)
+</a>
+</li>
+</ul>
+</div>
+<div class="dfn-panel" hidden="" role="dialog" aria-modal="true" id="dfn-panel-for-dfn-tm" aria-label= "Links in this document to definition: TM">
+<div>
+<a class="self-link" href="#dfn-tm" aria-label= "Permalink for definition: TM. Activate to close this dialog.">
+Permalink
+</a>
+</div>
+<p>
+<b>
+Referenced
+in:
+</b>
+</p>
+<ul>
+<li>
+Not
+referenced
+in
+this
+document.
+</li>
+</ul>
+</div>
+<div class="dfn-panel" hidden="" role="dialog" aria-modal="true" id="dfn-panel-for-dfn-property" aria-label= "Links in this document to definition: Property">
+<div>
+<a class="self-link" href="#dfn-property" aria-label= "Permalink for definition: Property. Activate to close this dialog.">
+Permalink
+</a>
+</div>
+<p>
+<b>
+Referenced
+in:
+</b>
+</p>
+<ul>
+<li>
+Not
+referenced
+in
+this
+document.
+</li>
+</ul>
+</div>
+<div class="dfn-panel" hidden="" role="dialog" aria-modal="true" id="dfn-panel-for-dfn-action" aria-label= "Links in this document to definition: Action">
+<div>
+<a class="self-link" href="#dfn-action" aria-label= "Permalink for definition: Action. Activate to close this dialog.">
+Permalink
+</a>
+</div>
+<p>
+<b>
+Referenced
+in:
+</b>
+</p>
+<ul>
+<li>
+Not
+referenced
+in
+this
+document.
+</li>
+</ul>
+</div>
+<div class="dfn-panel" hidden="" role="dialog" aria-modal="true" id="dfn-panel-for-dfn-event" aria-label= "Links in this document to definition: Event">
+<div>
+<a class="self-link" href="#dfn-event" aria-label= "Permalink for definition: Event. Activate to close this dialog.">
+Permalink
+</a>
+</div>
+<p>
+<b>
+Referenced
+in:
+</b>
+</p>
+<ul>
+<li>
+Not
+referenced
+in
+this
+document.
+</li>
+</ul>
+</div>
+<div class="dfn-panel" hidden="" role="dialog" aria-modal="true" id="dfn-panel-for-dfn-wot-anonymous-thing-description" aria-label= "Links in this document to definition: Anonymous TD">
+<div>
+<a class="self-link" href= "#dfn-wot-anonymous-thing-description" aria-label= "Permalink for definition: Anonymous TD. Activate to close this dialog.">
+Permalink
+</a>
+</div>
+<p>
+<b>
+Referenced
+in:
+</b>
+</p>
+<ul>
+<li>
+<a href="#ref-for-dfn-wot-anonymous-thing-description-1" title= "§ 7.3.1.3 Anonymous TD Identifiers">
+§
+7.3.1.3
+Anonymous
+TD
+Identifiers
+</a>
+</li>
+<li>
+<a href="#ref-for-dfn-wot-anonymous-thing-description-2" title= "§ 7.3.2.1.1 Creation">
+§
+7.3.2.1.1
+Creation
+</a>
+<a href= "#ref-for-dfn-wot-anonymous-thing-description-3" title= "Reference 2">
+(2)
+</a>
+<a href= "#ref-for-dfn-wot-anonymous-thing-description-4" title= "Reference 3">
+(3)
+</a>
+<a href= "#ref-for-dfn-wot-anonymous-thing-description-5" title= "Reference 4">
+(4)
+</a>
+<a href= "#ref-for-dfn-wot-anonymous-thing-description-6" title= "Reference 5">
+(5)
+</a>
+</li>
+<li>
+<a href="#ref-for-dfn-wot-anonymous-thing-description-7" title= "§ 7.3.2.1.2 Retrieval">
+§
+7.3.2.1.2
+Retrieval
+</a>
+</li>
+</ul>
+</div>
+<div class="dfn-panel" hidden="" role="dialog" aria-modal="true" id="dfn-panel-for-dfn-wot-discoverer" aria-label= "Links in this document to definition: Discoverer">
+<div>
+<a class="self-link" href="#dfn-wot-discoverer" aria-label= "Permalink for definition: Discoverer. Activate to close this dialog.">
+Permalink
+</a>
+</div>
+<p>
+<b>
+Referenced
+in:
+</b>
+</p>
+<ul>
+<li>
+<a href="#ref-for-dfn-wot-discoverer-1" title= "§ 5. Discoverer Process">
+§
+5.
+Discoverer
+Process
+</a>
+</li>
+<li>
+<a href="#ref-for-dfn-wot-discoverer-2" title= "§ 7.3.2.1.1 Creation">
+§
+7.3.2.1.1
+Creation
+</a>
+</li>
+</ul>
+</div>
+<div class="dfn-panel" hidden="" role="dialog" aria-modal="true" id="dfn-panel-for-dfn-wot-discovery" aria-label= "Links in this document to definition: Discovery">
+<div>
+<a class="self-link" href="#dfn-wot-discovery" aria-label= "Permalink for definition: Discovery. Activate to close this dialog.">
+Permalink
+</a>
+</div>
+<p>
+<b>
+Referenced
+in:
+</b>
+</p>
+<ul>
+<li>
+Not
+referenced
+in
+this
+document.
+</li>
+</ul>
+</div>
+<div class="dfn-panel" hidden="" role="dialog" aria-modal="true" id="dfn-panel-for-dfn-wot-exploration" aria-label= "Links in this document to definition: Exploration">
+<div>
+<a class="self-link" href="#dfn-wot-exploration" aria-label= "Permalink for definition: Exploration. Activate to close this dialog.">
+Permalink
+</a>
+</div>
+<p>
+<b>
+Referenced
+in:
+</b>
+</p>
+<ul>
+<li>
+Not
+referenced
+in
+this
+document.
+</li>
+</ul>
+</div>
+<div class="dfn-panel" hidden="" role="dialog" aria-modal="true" id="dfn-panel-for-dfn-wot-introduction" aria-label= "Links in this document to definition: Introduction">
+<div>
+<a class="self-link" href="#dfn-wot-introduction" aria-label= "Permalink for definition: Introduction. Activate to close this dialog.">
+Permalink
+</a>
+</div>
+<p>
+<b>
+Referenced
+in:
+</b>
+</p>
+<ul>
+<li>
+Not
+referenced
+in
+this
+document.
+</li>
+</ul>
+</div>
+<div class="dfn-panel" hidden="" role="dialog" aria-modal="true" id="dfn-panel-for-dfn-wot-thing-description-server" aria-label= "Links in this document to definition: Thing Description Server">
+<div>
+<a class="self-link" href="#dfn-wot-thing-description-server" aria-label= "Permalink for definition: Thing Description Server. Activate to close this dialog.">
+Permalink
+</a>
+</div>
+<p>
+<b>
+Referenced
+in:
+</b>
+</p>
+<ul>
+<li>
+Not
+referenced
+in
+this
+document.
+</li>
+</ul>
+</div>
+<div class="dfn-panel" hidden="" role="dialog" aria-modal="true" id="dfn-panel-for-dfn-wot-td-server" aria-label= "Links in this document to definition: TD Server">
+<div>
+<a class="self-link" href="#dfn-wot-td-server" aria-label= "Permalink for definition: TD Server. Activate to close this dialog.">
+Permalink
+</a>
+</div>
+<p>
+<b>
+Referenced
+in:
+</b>
+</p>
+<ul>
+<li>
+<a href="#ref-for-dfn-wot-td-server-1" title="§ 7.1 Overview">
+§
+7.1
+Overview
+</a>
+</li>
+</ul>
+</div>
+<div class="dfn-panel" hidden="" role="dialog" aria-modal="true" id="dfn-panel-for-dfn-wot-thing-description-directory" aria-label= "Links in this document to definition: Thing Description Directory">
+<div>
+<a class="self-link" href= "#dfn-wot-thing-description-directory" aria-label= "Permalink for definition: Thing Description Directory. Activate to close this dialog.">
+Permalink
+</a>
+</div>
+<p>
+<b>
+Referenced
+in:
+</b>
+</p>
+<ul>
+<li>
+<a href="#ref-for-dfn-wot-thing-description-directory-1" title= "§ 6. Introduction Mechanisms">
+§
+6.
+Introduction
+Mechanisms
+</a>
+<a href="#ref-for-dfn-wot-thing-description-directory-2" title= "Reference 2">
+(2)
+</a>
+</li>
+<li>
+<a href="#ref-for-dfn-wot-thing-description-directory-3" title= "§ 6.1 Direct">
+§
+6.1
+Direct
+</a>
+<a href= "#ref-for-dfn-wot-thing-description-directory-4" title= "Reference 2">
+(2)
+</a>
+</li>
+<li>
+<a href="#ref-for-dfn-wot-thing-description-directory-5" title= "§ 6.2 Well-Known URIs">
+§
+6.2
+Well-Known
+URIs
+</a>
+<a href= "#ref-for-dfn-wot-thing-description-directory-6" title= "Reference 2">
+(2)
+</a>
+</li>
+<li>
+<a href="#ref-for-dfn-wot-thing-description-directory-7" title= "§ 6.3 DNS-Based Service Discovery">
+§
+6.3
+DNS-Based
+Service
+Discovery
+</a>
+<a href= "#ref-for-dfn-wot-thing-description-directory-8" title= "Reference 2">
+(2)
+</a>
+<a href= "#ref-for-dfn-wot-thing-description-directory-9" title= "Reference 3">
+(3)
+</a>
+<a href= "#ref-for-dfn-wot-thing-description-directory-10" title= "Reference 4">
+(4)
+</a>
+</li>
+<li>
+<a href="#ref-for-dfn-wot-thing-description-directory-11" title="§ 6.4 CoRE Link Format and CoRE Resource Directory">
+§
+6.4
+CoRE
+Link
+Format
+and
+CoRE
+Resource
+Directory
+</a>
+<a href= "#ref-for-dfn-wot-thing-description-directory-12" title= "Reference 2">
+(2)
+</a>
+<a href= "#ref-for-dfn-wot-thing-description-directory-13" title= "Reference 3">
+(3)
+</a>
+</li>
+<li>
+<a href="#ref-for-dfn-wot-thing-description-directory-14" title="§ 6.5 DID Documents">
+§
+6.5
+DID
+Documents
+</a>
+<a href= "#ref-for-dfn-wot-thing-description-directory-15" title= "Reference 2">
+(2)
+</a>
+<a href= "#ref-for-dfn-wot-thing-description-directory-16" title= "Reference 3">
+(3)
+</a>
+<a href= "#ref-for-dfn-wot-thing-description-directory-17" title= "Reference 4">
+(4)
+</a>
+</li>
+<li>
+<a href="#ref-for-dfn-wot-thing-description-directory-18" title="§ 7.1 Overview">
+§
+7.1
+Overview
+</a>
+<a href= "#ref-for-dfn-wot-thing-description-directory-19" title= "Reference 2">
+(2)
+</a>
+</li>
+<li>
+<a href="#ref-for-dfn-wot-thing-description-directory-20" title="§ 7.3 Thing Description Directory">
+§
+7.3
+Thing
+Description
+Directory
+</a>
+</li>
+<li>
+<a href="#ref-for-dfn-wot-thing-description-directory-21" title="§ 7.3.1 Information Model">
+§
+7.3.1
+Information
+Model
+</a>
+</li>
+<li>
+<a href="#ref-for-dfn-wot-thing-description-directory-22" title="§ 7.3.1.1 Registration Information">
+§
+7.3.1.1
+Registration
+Information
+</a>
+</li>
+<li>
+<a href="#ref-for-dfn-wot-thing-description-directory-23" title="§ 11.3 CoRE Resource Types Registration">
+§
+11.3
+CoRE
+Resource
+Types
+Registration
+</a>
+</li>
+<li>
+<a href="#ref-for-dfn-wot-thing-description-directory-24" title="§ 12.1 DID Service Name Registration">
+§
+12.1
+DID
+Service
+Name
+Registration
+</a>
+</li>
+</ul>
+</div>
+<div class="dfn-panel" hidden="" role="dialog" aria-modal="true" id="dfn-panel-for-dfn-wot-tdd" aria-label= "Links in this document to definition: TDD">
+<div>
+<a class="self-link" href="#dfn-wot-tdd" aria-label= "Permalink for definition: TDD. Activate to close this dialog.">
+Permalink
+</a>
+</div>
+<p>
+<b>
+Referenced
+in:
+</b>
+</p>
+<ul>
+<li>
+<a href="#ref-for-dfn-wot-tdd-1" title= "§ A. JSON Schema for WoT Discovery TD-extensions">
+§
+A.
+JSON
+Schema
+for
+WoT
+Discovery
+TD-extensions
+</a>
+</li>
+</ul>
+</div>
+<div class="dfn-panel" hidden="" role="dialog" aria-modal="true" id="dfn-panel-for-dfn-wot-partial-thing-description" aria-label= "Links in this document to definition: Partial TD">
+<div>
+<a class="self-link" href="#dfn-wot-partial-thing-description" aria-label= "Permalink for definition: Partial TD. Activate to close this dialog.">
+Permalink
+</a>
+</div>
+<p>
+<b>
+Referenced
+in:
+</b>
+</p>
+<ul>
+<li>
+<a href="#ref-for-dfn-wot-partial-thing-description-1" title= "§ 7.3.2.1.3 Update">
+§
+7.3.2.1.3
+Update
+</a>
+</li>
+<li>
+<a href="#ref-for-dfn-wot-partial-thing-description-2" title= "§ 7.3.2.2 Events API">
+§
+7.3.2.2
+Events
+API
+</a>
+<a href= "#ref-for-dfn-wot-partial-thing-description-3" title= "Reference 2">
+(2)
+</a>
+</li>
+</ul>
+</div>
+<div class="dfn-panel" hidden="" role="dialog" aria-modal="true" id="dfn-panel-for-dfn-wot-enriched-thing-description" aria-label= "Links in this document to definition: Enriched TD">
+<div>
+<a class="self-link" href= "#dfn-wot-enriched-thing-description" aria-label= "Permalink for definition: Enriched TD. Activate to close this dialog.">
+Permalink
+</a>
+</div>
+<p>
+<b>
+Referenced
+in:
+</b>
+</p>
+<ul>
+<li>
+<a href="#ref-for-dfn-wot-enriched-thing-description-1" title= "§ 7.3.1 Information Model">
+§
+7.3.1
+Information
+Model
+</a>
+</li>
+<li>
+<a href="#ref-for-dfn-wot-enriched-thing-description-2" title= "§ 7.3.1.1 Registration Information">
+§
+7.3.1.1
+Registration
+Information
+</a>
+<a href= "#ref-for-dfn-wot-enriched-thing-description-3" title= "Reference 2">
+(2)
+</a>
+</li>
+<li>
+<a href="#ref-for-dfn-wot-enriched-thing-description-4" title= "§ 7.3.2.1.2 Retrieval">
+§
+7.3.2.1.2
+Retrieval
+</a>
+<a href= "#ref-for-dfn-wot-enriched-thing-description-5" title= "Reference 2">
+(2)
+</a>
+</li>
+<li>
+<a href="#ref-for-dfn-wot-enriched-thing-description-6" title= "§ 7.3.2.1.6 Validation">
+§
+7.3.2.1.6
+Validation
+</a>
+</li>
+<li>
+<a href="#ref-for-dfn-wot-enriched-thing-description-7" title= "§ A. JSON Schema for WoT Discovery TD-extensions">
+§
+A.
+JSON
+Schema
+for
+WoT
+Discovery
+TD-extensions
+</a>
+</li>
+</ul>
+</div>
+<script id="respec-dfn-panel">
+<![CDATA[ (() =>
+{
+//
+@ts-check
+if
+(document.respec)
+{
+document.respec.ready.then(setupPanel);
+}
+else
+{
+setupPanel();
+}
+function
+setupPanel()
+{
+const
+listener
+=
+panelListener();
+document.body.addEventListener("keydown",
+listener);
+document.body.addEventListener("click",
+listener);
+}
+function
+panelListener()
+{
+/**
+@type
+{HTMLElement}
+*/
+let
+panel
+=
+null;
+return
+event
+=>
+{
+const
+{
+target,
+type
+}
+=
+event;
+if
+(!(target
+instanceof
+HTMLElement))
+return;
+//
+For
+keys,
+we
+only
+care
+about
+Enter
+key
+to
+activate
+the
+panel
+//
+otherwise
+it's
+activated
+via
+a
+click.
+if
+(type
+===
+"keydown"
+&&
+event.key
+!==
+"Enter")
+return;
+const
+action
+=
+deriveAction(event);
+switch
+(action)
+{
+case
+"show":
+{
+hidePanel(panel);
+/**
+@type
+{HTMLElement}
+*/
+const
+dfn
+=
+target.closest("dfn,
+.index-term");
+panel
+=
+document.getElementById(`dfn-panel-for-${dfn.id}`);
+const
+coords
+=
+deriveCoordinates(event);
+displayPanel(dfn,
+panel,
+coords);
+break;
+}
+case
+"dock":
+{
+panel.style.left
+=
+null;
+panel.style.top
+=
+null;
+panel.classList.add("docked");
+break;
+}
+case
+"hide":
+{
+hidePanel(panel);
+panel
+=
+null;
+break;
+}
+}
+};
+}
+/**
+*
+@param
+{MouseEvent|KeyboardEvent}
+event
+*/
+function
+deriveCoordinates(event)
+{
+const
+target
+=
+/**
+@type
+HTMLElement
+*/
+(event.target);
+//
+We
+prevent
+synthetic
+AT
+clicks
+from
+putting
+//
+the
+dialog
+in
+a
+weird
+place.
+The
+AT
+events
+sometimes
+//
+lack
+coordinates,
+so
+they
+have
+clientX/Y
+=
+0
+const
+rect
+=
+target.getBoundingClientRect();
+if
+(
+event
+instanceof
+MouseEvent
+&&
+event.clientX
+>
+=
+rect.left
+&&
+event.clientY
+>
+=
+rect.top
+)
+{
+//
+The
+event
+probably
+happened
+inside
+the
+bounding
+rect...
+return
+{
+x:
+event.clientX,
+y:
+event.clientY
+};
+}
+//
+Offset
+to
+the
+middle
+of
+the
+element
+const
+x
+=
+rect.x
++
+rect.width
+/
+2;
+//
+Placed
+at
+the
+bottom
+of
+the
+element
+const
+y
+=
+rect.y
++
+rect.height;
+return
+{
+x,
+y
+};
+}
+/**
+*
+@param
+{Event}
+event
+*/
+function
+deriveAction(event)
+{
+const
+target
+=
+/**
+@type
+{HTMLElement}
+*/
+(event.target);
+const
+hitALink
+=
+!!target.closest("a");
+if
+(target.closest("dfn:not([data-cite]),
+.index-term"))
+{
+return
+hitALink
+?
+"none"
+:
+"show";
+}
+if
+(target.closest(".dfn-panel"))
+{
+if
+(hitALink)
+{
+return
+target.classList.contains("self-link")
+?
+"hide"
+:
+"dock";
+}
+const
+panel
+=
+target.closest(".dfn-panel");
+return
+panel.classList.contains("docked")
+?
+"hide"
+:
+"none";
+}
+if
+(document.querySelector(".dfn-panel:not([hidden])"))
+{
+return
+"hide";
+}
+return
+"none";
+}
+/**
+*
+@param
+{HTMLElement}
+dfn
+*
+@param
+{HTMLElement}
+panel
+*
+@param
+{{
+x:
+number,
+y:
+number
+}}
+clickPosition
+*/
+function
+displayPanel(dfn,
+panel,
+{
+x,
+y
+})
+{
+panel.hidden
+=
+false;
+//
+distance
+(px)
+between
+edge
+of
+panel
+and
+the
+pointing
+triangle
+(caret)
+const
+MARGIN
+=
+20;
+const
+dfnRects
+=
+dfn.getClientRects();
+//
+Find
+the
+`top`
+offset
+when
+the
+`dfn`
+can
+be
+spread
+across
+multiple
+lines
+let
+closestTop
+=
+0;
+let
+minDiff
+=
+Infinity;
+for
+(const
+rect
+of
+dfnRects)
+{
+const
+{
+top,
+bottom
+}
+=
+rect;
+const
+diffFromClickY
+=
+Math.abs((top
++
+bottom)
+/
+2
+-
+y);
+if
+(diffFromClickY
+< minDiff) { minDiff = diffFromClickY; closestTop = top; } } const top = window.scrollY + closestTop + dfnRects[0].height; const left = x - MARGIN; panel.style.left = `${left}px`; panel.style.top = `${top}px`; // Find if the panel is flowing out of the window const panelRect = panel.getBoundingClientRect(); const SCREEN_WIDTH = Math.min(window.innerWidth, window.screen.width); if (panelRect.right >
+SCREEN_WIDTH)
+{
+const
+newLeft
+=
+Math.max(MARGIN,
+x
++
+MARGIN
+-
+panelRect.width);
+const
+newCaretOffset
+=
+left
+-
+newLeft;
+panel.style.left
+=
+`${newLeft}px`;
+/**
+@type
+{HTMLElement}
+*/
+const
+caret
+=
+panel.querySelector(".caret");
+caret.style.left
+=
+`${newCaretOffset}px`;
+}
+//
+As
+it's
+a
+dialog,
+we
+trap
+focus.
+//
+TODO:
+when
+<dialog>
+becomes
+a
+implemented,
+we
+should
+really
+//
+use
+that.
+trapFocus(panel,
+dfn);
+}
+/**
+*
+@param
+{HTMLElement}
+panel
+*
+@param
+{HTMLElement}
+dfn
+*
+@returns
+*/
+function
+trapFocus(panel,
+dfn)
+{
+/**
+@type
+NodeListOf
+<HTMLAnchorElement>
+elements
+*/
+const
+anchors
+=
+panel.querySelectorAll("a[href]");
+//
+No
+need
+to
+trap
+focus
+if
+(!anchors.length)
+return;
+//
+Move
+focus
+to
+first
+anchor
+element
+const
+first
+=
+anchors.item(0);
+first.focus();
+const
+trapListener
+=
+createTrapListener(anchors,
+panel,
+dfn);
+panel.addEventListener("keydown",
+trapListener);
+//
+Hiding
+the
+panel
+releases
+the
+trap
+const
+mo
+=
+new
+MutationObserver(records
+=>
+{
+const
+[record]
+=
+records;
+const
+target
+=
+/**
+@type
+HTMLElement
+*/
+(record.target);
+if
+(target.hidden)
+{
+panel.removeEventListener("keydown",
+trapListener);
+mo.disconnect();
+}
+});
+mo.observe(panel,
+{
+attributes:
+true,
+attributeFilter:
+["hidden"]
+});
+}
+/**
+*
+*
+@param
+{NodeListOf
+<HTMLAnchorElement>
+}
+anchors
+*
+@param
+{HTMLElement}
+panel
+*
+@param
+{HTMLElement}
+dfn
+*
+@returns
+*/
+function
+createTrapListener(anchors,
+panel,
+dfn)
+{
+const
+lastIndex
+=
+anchors.length
+-
+1;
+let
+currentIndex
+=
+0;
+return
+event
+=>
+{
+switch
+(event.key)
+{
+//
+Hitting
+"Tab"
+traps
+us
+in
+a
+nice
+loop
+around
+elements.
+case
+"Tab":
+{
+event.preventDefault();
+currentIndex
++=
+event.shiftKey
+?
+-1
+:
++1;
+if
+(currentIndex
+< 0) { currentIndex = lastIndex; } else if (currentIndex >
+lastIndex)
+{
+currentIndex
+=
+0;
+}
+anchors.item(currentIndex).focus();
+break;
+}
+//
+Hitting
+"Enter"
+on
+an
+anchor
+releases
+the
+trap.
+case
+"Enter":
+hidePanel(panel);
+break;
+//
+Hitting
+"Escape"
+returns
+focus
+to
+dfn.
+case
+"Escape":
+hidePanel(panel);
+dfn.focus();
+return;
+}
+};
+}
+/**
+@param
+{HTMLElement}
+panel
+*/
+function
+hidePanel(panel)
+{
+if
+(!panel)
+return;
+panel.hidden
+=
+true;
+panel.classList.remove("docked");
+}
+})()
+]]>
+</script>
+<script src="https://www.w3.org/scripts/TR/2021/fixup.js">
+</script>
+</body>
+</html>
diff --git a/publication/6-rec/index.html b/publication/6-rec/index.html
index 83f66682..fd50e706 100644
--- a/publication/6-rec/index.html
+++ b/publication/6-rec/index.html
@@ -24,7 +24,7 @@
         inlineCSS: true,
         noIDLIn: true,
         specStatus : "REC",
-        publishDate: "2023-11-30",
+        publishDate: "2023-12-05",
         implementationReportURI: "https://w3c.github.io/wot-discovery/testing/report.html",
         errata: "https://w3c.github.io/wot-discovery/errata.html",
         shortName : "wot-discovery",
diff --git a/publication/6-rec/static.html b/publication/6-rec/static.html
index 901ef250..4659504c 100644
--- a/publication/6-rec/static.html
+++ b/publication/6-rec/static.html
@@ -165,7 +165,7 @@
   "name": "Web of Things (WoT) Discovery",
   "inLanguage": "en-US",
   "license": "https://www.w3.org/copyright/software-license-2023/",
-  "datePublished": "2023-11-30",
+  "datePublished": "2023-12-05",
   "copyrightHolder": {
     "name": "World Wide Web Consortium",
     "url": "https://www.w3.org/"
@@ -990,7 +990,7 @@
   "inlineCSS": true,
   "noIDLIn": true,
   "specStatus": "REC",
-  "publishDate": "2023-11-30",
+  "publishDate": "2023-12-05",
   "implementationReportURI": "https://w3c.github.io/wot-discovery/testing/report.html",
   "errata": "https://w3c.github.io/wot-discovery/errata.html",
   "shortName": "wot-discovery",
@@ -1137,20 +1137,20 @@
       "id": "amplification-attacks"
     }
   },
-  "publishISODate": "2023-11-30T00:00:00.000Z",
-  "generatedSubtitle": "W3C Recommendation 30 November 2023"
+  "publishISODate": "2023-12-05T00:00:00.000Z",
+  "generatedSubtitle": "W3C Recommendation 05 December 2023"
 }</script>
 <link rel="stylesheet" href="https://www.w3.org/StyleSheets/TR/2021/W3C-REC"></head>
 <body class="h-entry toc-inline"><div class="head">
     <p class="logos"><a class="logo" href="https://www.w3.org/"><img crossorigin="" alt="W3C" height="48" src="https://www.w3.org/StyleSheets/TR/2021/logos/W3C" width="72">
   </a></p>
     <h1 id="title" class="title">Web of Things (WoT) Discovery</h1> 
-    <p id="w3c-state"><a href="https://www.w3.org/standards/types#REC">W3C Recommendation</a> <time class="dt-published" datetime="2023-11-30">30 November 2023</time></p>
+    <p id="w3c-state"><a href="https://www.w3.org/standards/types#REC">W3C Recommendation</a> <time class="dt-published" datetime="2023-12-05">05 December 2023</time></p>
     <details open="">
       <summary>More details about this document</summary>
       <dl>
         <dt>This version:</dt><dd>
-                <a class="u-url" href="https://www.w3.org/TR/2023/REC-wot-discovery-20231130/">https://www.w3.org/TR/2023/REC-wot-discovery-20231130/</a>
+                <a class="u-url" href="https://www.w3.org/TR/2023/REC-wot-discovery-20231205/">https://www.w3.org/TR/2023/REC-wot-discovery-20231205/</a>
               </dd>
         <dt>Latest published version:</dt><dd>
                 <a href="https://www.w3.org/TR/wot-discovery/">https://www.w3.org/TR/wot-discovery/</a>