Include inter-class relationship graph in schema documentation

Makefile

@@ -168,8 +168,9 @@ $(DOCDIR):
 
 # Compile static Markdown files, images, and JavaScript scripts, into a documentation website.
 #
-# Then, use `refgraph` (part of `refscan`) to generate a diagram (i.e. a graph that depicts
-# inter-collection relationships) in the documentation website's file tree.
+# Then, use `refgraph` (part of `refscan`) to generate a pair of diagrams within the website's file tree.
+# One of the diagrams is a graph showing all the _inter-collection_ relationships the schema says can exist,
+# and the other diagram is a graph showing all the _inter-class_ relationships the schema says can exist.
 gendoc: $(DOCDIR) prefixmaps
 	# Copy all documentation files to the documentation directory
 	cp -rf $(SRC)/docs/* $(DOCDIR)
@@ -181,9 +182,11 @@ gendoc: $(DOCDIR) prefixmaps
 	# Create directory for JavaScript files and copy them
 	mkdir -p $(DOCDIR)/javascripts
 	$(RUN) cp $(SRC)/scripts/*.js $(DOCDIR)/javascripts/
-	# Use `refgraph` to generate an interactive diagram within the compiled documentation website file tree.
+	# Use `refgraph` (part of `refscan`) to generate diagrams within the website's file tree.
 	mkdir -p $(DOCDIR)/visualizations
 	$(RUN) refgraph --schema nmdc_schema/nmdc_materialized_patterns.yaml --subject collection --graph $(DOCDIR)/visualizations/collection-graph.html
+	$(RUN) refgraph --schema nmdc_schema/nmdc_materialized_patterns.yaml --subject class      --graph $(DOCDIR)/visualizations/class-graph.html
+
 testdoc: gendoc serve
 
 MKDOCS = $(RUN) mkdocs

src/docs/visualizations.md

@@ -11,3 +11,15 @@ Each circle represents a collection.
 Each arrow represents all of the fields that documents in one collection—the one at that arrow's tail—can
 use to refer to documents in another collection—the one at that arrow's head.
 If you click on a circle, the names of the fields will appear on the arrows connected to that circle.
+
+## Inter-class relationship diagram
+
+<!-- Note: `visualizations/class-graph.html` does not exist in the source code repository.
+           It gets generated as part of the documentation build process. -->
+This [**inter-class relationship diagram**](visualizations/class-graph.html)
+shows the **classes** defined within the schema, and the **relationships** between those classes.
+
+Each circle represents a class.
+Each arrow represents all of the slots that instances of that class—the one at that arrow's tail—can
+use to refer to instances of another class—the one at that arrow's head.
+If you click on a circle, the names of the slots will appear on the arrows connected to that circle.