Question

I have a particular Class URI for which I am trying to get an OntClass. The model is a regular model.

I wrote some code to find out whether the right statements were in the model, and it seems that they are so I can’t understand why it won’t let me view this as an OntClass. (tblURI is a String passed as a method parameter)

Resource tblR = m.createResource(tblURI);
List<Statement> prp = tblR.listProperties().toList();
for(Statement s : prp)
    System.out.println(s);
System.out.println(tblR.canAs(OntClass.class));
OntClass tbl = tblR.as(OntClass.class);

This is the output:

[kps:datasource/EnsembleMS#translation_stable_id, http://www.w3.org/1999/02/22-rdf-syntax-ns#type, http://www.w3.org/2002/07/owl#Class]
[kps:datasource/EnsembleMS#translation_stable_id, http://www.w3.org/1999/02/22-rdf-syntax-ns#type, http://www.w3.org/2000/01/rdf-schema#Class]
[kps:datasource/EnsembleMS#translation_stable_id, http://www.w3.org/2000/01/rdf-schema#isDefinedBy, kps:datasource/EnsembleMS]
[kps:datasource/EnsembleMS#translation_stable_id, http://www.w3.org/2000/01/rdf-schema#label, "translation_stable_id"]
false
com.hp.hpl.jena.ontology.ConversionException: Cannot convert node kps:datasource/EnsembleMS#translation_stable_id to OntClass: it does not have rdf:type owl:Class or equivalent
    at com.hp.hpl.jena.ontology.impl.OntClassImpl$1.wrap(OntClassImpl.java:81)
    at com.hp.hpl.jena.enhanced.EnhNode.convertTo(EnhNode.java:155)
    at com.hp.hpl.jena.enhanced.EnhNode.convertTo(EnhNode.java:34)
    at com.hp.hpl.jena.enhanced.Polymorphic.asInternal(Polymorphic.java:66)
    at com.hp.hpl.jena.enhanced.EnhNode.as(EnhNode.java:110)
    at com.KPS.myApp.exampleMethod(myApp.java:123)

Why is it throwing an exception and how can I get an OntClass for the resource with uri tblURI?

Thanks for any pointers

Answer 1

You don’t say what kind of model m is. In particular, if m was created with the RDFS language profile, the OntModel will be looking for an rdf:type of rdfs:Class, not owl:Class. If that’s not the issue, then a complete minimal (i.e. runnable) example would help.

By the way, there’s another problem I can see: resource URI’s in the model should be in absolute form, not abbreviated form. The fact that you’ve got q-name URI’s in your model, like kps:datasource/EnsembleMS#translation_stable_id, suggest that something is going wrong with your prefix handling. That won’t by itself cause the problem you’ve reported, but it’s a red flag to investigate.

Update

Responding to questions:

• yes, you need to be using an OntModel, otherwise it’s not possible for the OntClass to know which langauge profile to use. Either create the model as OntModel in the first place:

  OntModel m = modelFactory.createOntologyModel( OntModelSpec.OWL_MEM );
  

  or wrap your plain model as an OntModel:

  OntModel om = modelFactory.createOntologyModel( OntModelSpec.OWM_MEM, m );
  

  Of course, you many use any of the model specifications, as you please, OWL_MEM is just one option.

• createResource will not expand prefixes for you. So, you should expand them yourself before creating the resource:

  m.createResource( m.expandPrefix( "foo:bar" ) );
  

  Of course, this requires the prefix "foo" to be registered as a prefix. This happens automatically if you read an RDF document that defines the prefix in its syntax, but otherwise can be done manually with setNsPrefix.