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N3 to JSON-LD converter

Parse N3 (not just turtle) and converts it to JSON-LD. That JSON-LD can also be converted back to N3, though not all JSON-LD features are supported in that conversion (but everything that gets output by the parser can be converted back).

Usage

Install with npm using npm install n3-parser.js.

const N3Parser = require('n3-parser.js').N3Parser;

let parser = new N3Parser();
let jsonld = parser.toJSONLD(`PREFIX dc: <http://purl.org/dc/elements/1.1/>
    <http://en.wikipedia.org/wiki/Tony_Benn>
    dc:title "Tony Benn";
    dc:publisher "Wikipedia".
`);
console.log(jsonld);

// Output:
// { '@context': { dc: 'http://purl.org/dc/elements/1.1/' },
//  '@id': 'http://en.wikipedia.org/wiki/Tony_Benn',
//  'dc:title': 'Tony Benn',
//  'dc:publisher': 'Wikipedia' }

const JSONLDParser = require('n3-parser.js').JSONLDParser;
let jsonldParser = new JSONLDParser();
let n3 = jsonldParser.toN3(jsonld);
console.log(n3);

// Output:
// PREFIX dc: <http://purl.org/dc/elements/1.1/>
// <http://en.wikipedia.org/wiki/Tony_Benn> dc:title "Tony Benn" ;
// dc:publisher "Wikipedia" .

N3 features

N3 has several features that are not covered by JSON-LD. In those cases we made some adaptations to the JSON-LD syntax. This also means that the output is not valid JSON-LD (but can still be converted back to N3 by our parser).

Formulas

For N3 formulas we use JSON-LD graphs without an @id. These do have semantic differences though, which should be taken into account. (JSON-LD treats these as graphs with a blank node as identifier).

=>

=> gets translated to its corresponding URI log:implies.

Literal/formula subjects

JSON-LD only supports URIs in the subject position. For literals we solve this by allowing JSON-LD @value objects to also have predicates:

PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
"Apple" rdfs:label "red" .
{ "@context": { "rdfs": "http://www.w3.org/2000/01/rdf-schema#" },
  "@value": "Apple",
  "rdfs:label": "red" }

Similarly, for formulas we allow JSON-LD graphs to have predicates:

PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
{} rdfs:label "red" .
{ "@context": { "rdfs": "http://www.w3.org/2000/01/rdf-schema#" },
  "@graph": [],
  "rdfs:label": "red" }

Variables

JSON-LD has no variables. We use the same syntax as URIs for those, e.g.:

{ "@id": "?b" }

Literal/formula predicates

JSON-LD only supports URIs in the predicate position, while N3 allows all terms there. The solution there is a bit more convoluted. We replace the offending predicate by a newly generated blank node, and also create a new object containing both the blank node and its corresponding value (or graph).

PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
?a "predicate" ?b .
{
  "@context": {
    "rdfs": "http://www.w3.org/2000/01/rdf-schema#"
  },
  "@graph": [
    {
      "@value": "predicate",
      "@id": "_:b_01a89c31-59be-4aef-a7f5-708f33917877"
    },
    {
      "@id": "?a",
      "_:b_01a89c31-59be-4aef-a7f5-708f33917877": {
        "@id": "?b"
      }
    }
  ]
}

Base

JSON-LD has no good way to represent an empty prefix (e.g. :a). We replace all such prefixes with #base, which allows us to retain the empty prefix when converting back to N3.

PREFIX : <http://example.com/>
:s :p ?o .
{
  "@context": {
    "#base": "http://example.com/"
  },
  "@id": "#base:s",
  "#base:p": {
    "@id": "?o"
  }
}