kinow commented on a change in pull request #11: URL: https://github.com/apache/jena-site/pull/11#discussion_r426916031
########## File path: source/documentation/rdfstar/__index.md ########## @@ -0,0 +1,118 @@ +--- +title: Support of RDF* +slug: index +--- +[RDF\*](https://arxiv.org/abs/1406.3399) 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](https://blog.liu.se/olafhartig/2019/01/10/position-statement-rdf-star-and-sparql-star/). + +Example: + +```turtle +<< :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\*. + +Support for RDF* is experimentation in Jena 3.15.0 (released May 2020): + +* 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 memory-based storage (graphs and datasets). +* Support in the Model API. + +All this is active by default in Fuseki. + +This support is experimental and subject to change. The aim is to follow the definition of RDF* as well as emerging _de facto_ consensus in other implementations. + +Later releases will extend support to persistent storage in [TDB1](/documentation/tdb) and [TDB2](/documentation/tdb2/). + +## 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: + +```sparql +SELECT ?name { <<:john foaf:name ?name >> dct:source <http://example/directory> } +``` + +Insert triples terms into the default graph to record the graph source. + +```sparql +INSERT { <<?s ?p ?o>> dct:source <http://example/directory> } +WHERE { + GRAPH <http://example/directory> { + ?s ?p ?o + } +} +``` + +### SPARQL Functions related to triple terms + +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 | + +### 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: + +```json + { + "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`: + +```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 are occur in the subject and object positions. Review comment: s/They are occur/They occur/? ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: us...@infra.apache.org
