How to Add Custom Predicate Support to Apache Jena Fuseki?

[Myasir92]

I'm using the Apache Jena Fuseki executable locally for data management, but I've noticed it lacks support for a valuable predicate from Sesame RDF4J. My goal is to incorporate this support by adding custom rules. While it's not as straightforward as using RDF4J directly, I am familiar with the predicate's rules and believe adding these custom rules to Fuseki is possible. Could you guide me on how to effectively add custom rules in Fuseki?

[ajs6f]

Hi @Myasir92, I'm not quite sure what you mean by "support for a ... predicate". Of which predicate are you thinking? Do you mean simply the use of the predicate? You should be able to use any well-formed predicate right away. Or is there a special semantic for this predicate in RDF4J that you would like to see enforced or enacted in your Fuseki instance? Please give us a little more context.

[ajs6f]

Okay, I'm now reading your question more carefully, and I see that you refer to rules. This is something that Jena can handle very well, and if you give us some specifics we can advise you more fully.

[Myasir92]

Hi @ajs6f I appreciate your quick response. I'd like to implement a feature similar to the 'directType' predicate of sesame RDF4J, which is supported in other triplestores like GraphDB. This feature is quite useful, but currently not available in Fuseki. My plan is to write a custom rule to enable this support within Fuseki.

[ajs6f]

Is this the inferencing regime you want to implement? IIUC you want to be able to query the explicitly declared rdf:type of entities without querying the inferred types?

[Myasir92]

@ajs6f Yeah

[afs]

https://jena.apache.org/documentation/inference/#directRelations

and I found this in the code which shows the way to name direct prediciates

jena/jena-core/src/main/java/org/apache/jena/reasoner/ReasonerRegistry.java

Line 177 in 4fb3ce2

public static String makeDirect( String uri )

Myasir92 -

This is one time when you may find the users@jena.apache.org useful because some people with expertise in the Jena rule system only have time to read and response there.

[Myasir92]

@afs Could you please provide an example of a SPARQL query that utilizes that predicate, or are there additional steps that need to be taken?

[ajs6f]

Thank you @afs!

This method on OntResource may also be useful (see the parameter):

jena/jena-core/src/main/java/org/apache/jena/ontology/OntResource.java

Line 533 in 4fb3ce2

public ExtendedIterator<Resource> listRDFTypes( boolean direct );