猫头鹰 从rdf提取ObjectProperty

Question

I'm trying to extract all the classes and the ObjectProperties from a .rdf file that cointains some rdf triple. I'm loading this file LUBM

OWLOntologyManager manager  = OWLManager.createOWLOntologyManager();
File ontFile = new File("C:\\Ontology\\University0_0.owl");
OWLOntology ont = manager.loadOntologyFromOntologyDocument(ontFile);
StructuralReasonerFactory factory = new StructuralReasonerFactory();
OWLReasoner reasoner = factory.createReasoner(ont);

Now I extract all the class:

 System.out.println("Class");
 for (OWLClass cls : ont.getClassesInSignature(Imports.EXCLUDED)){
     System.out.println(cls.toString());
 }

And now I extract all the ObjectProperty:

System.out.println("Role");
for (OWLObjectProperty obp : ont.getObjectPropertiesInSignature()){
    System.out.println(obp.toString());
}

I don't need all the classes and the properties of the ontology( LUBM Ontology ), but only the classes and the property that are used in the .rdf file. But ont.getObjectPropertiesInSignature() return a empty set. (I have the same problem with .rdf file from DBPedia.)

I know that I can use ont.getObjectPropertiesInSignature(Imports.INCLUDED) but I'm not interested to the properties of the ontology.

After this I need to do some query with SPARQL-DL and if I do the following query I haven't result.

SELECT DISTINCT ?x ?y WHERE { 
    PropertyValue(?x, <http://swat.cse.lehigh.edu/onto/univ-bench.owl#takesCourse>, ?y)
}

(I take http://swat.cse.lehigh.edu/onto/univ-bench.owl#takesCourse exploring the dataset manually)

But if I use Jena and do the above query with a SPARQL query all work and I have results.

SELECT DISTINCT ?x ?y 
WHERE{
?x <http://www.lehigh.edu/~zhp2/2004/0401/univ-bench.owl#takesCourse> ?y.
}

Answer 1

I cannot see any object property declaration in the file you have linked - this would likely stop them being listed.

Note that the SPARQL queries you have shown have different namespaces for the properties, so it's not surprising that they bring back different results.