Support of RDF*

RDF* is an extension to RDF that provides a way for one triple to refer to another triple. Another resource about RDF* is Olaf Hartig’s blog entry.

Example:

<< :john foaf:name "John Smith" >> dct:source <http://example/directory> .

The part << :john foaf:name "John Smith" >> is a triple term and refers to the triple with subject :john, property foaf:name and object "John Smith".

Triple terms can be in the subject or object position.

Jena provides support for RDF* and the related SPARQL*.

  • Turtle, N-Triples, TriG and N-Quads extended for Triple Terms syntax. There is no output in RDF/XML.
  • SPARQL extended with Triple Term syntax for graph matching (in code, use Syntax.syntaxARQ).
  • SPARQL Result formats for JSON and XML extended to support Triple Terms in results.
  • Support in the Model API.

All this is active by default in Fuseki.

The aim is to follow the definition of RDF* as well as emerging _de facto_ consensus in other implementations.

Storage in databases TDB1 and TDB2 is supported as of Jena 3.16.0.

RDF*

RDF* syntax for triple terms is added to the parsers for Turtle, N-Triples, TriG and N-Quads.

Datasets may have graphs that have triple terms that refer to triples anywhere, not just in the same graph.

SPARQL*

Matches for triple terms:

SELECT ?name { <<:john foaf:name ?name >> dct:source <http://example/directory> }

Insert triples terms into the default graph to record the graph source.

INSERT { <<?s ?p ?o>> dct:source <http://example/directory> }
WHERE {
    GRAPH <http://example/directory> {
        ?s ?p ?o
    }
}

These functions cause an expression error if passed the wrong type of arguments. afn: is a prefix for <http://jena.apache.org/ARQ/function#>.

Function Description
afn:subject(?t) Return the subject of the triple term
afn:predicate(?t) Return the predicate (property) of the triple term
afn:object(?t) Return the object of the triple term
afn:triple(?s, ?p, ?o) Create a triple term from s/p/o
afn:isTriple(?t) Return true if the argument value is a triple term

apf: is a prefix for <http://jena.apache.org/ARQ/property#>.

Property Function Description
<< s p o >> apf:find t . Match the triple term. Any s, p, o, and t can be RDF terms or variables.

apf:find will result in all the variables being set according to the match, If t is a variable, ?t, it is bound to a triple term for the match of <<s p o>>.

SPARQL results

The syntaxes for SPARQL results from a SELECT query, application/sparql-results+json, application/sparql-results+xml are extended to include triple terms:

The triple term << _:b0 <http://example/p> 123 >> is encoded, in application/sparql-results+json as:

    {
      "type": "triple" ,
      "value": {
        "subject":   { "type": "bnode" , "value": "b0" } ,
        "property":  { "type": "uri" , "value": "http://example/p" } ,
        "object":    { "type": "literal" , "datatype": "http://www.w3.org/2001/XMLSchema#integer" , "value": "123" }
    }

and similarly in application/sparql-results+xml:

    <triple>
      <subject>
        <bnode>b0</bnode>
      </subject>
      <property>
        <uri>http://example/p</uri>
      </property>
      <object>
        <literal datatype="http://www.w3.org/2001/XMLSchema#integer">123</literal>
      </object>
    </triple>

Model API

RDF* triple terms are treated as Resource to preserve the typed Model API. They occur in the subject and object positions.

A Resource contains a Statement object if the underlying RDF term is an RDF* triple term.

New methods include:

  • Statement Resource.getStatement()
  • Resource Model.createResource(Statement)
  • Resource ResourceFactory.createStatement