CODEWITHSUNDEEP
javajenaontology
Fopa Léon Constantin
Fopa Léon Constantin

Reputation: 12383

How to instantiate just one concept in an Ontology with Jena?

I'm working on how to automatically instantiate an ontology with Jena. I'm interested in instantiating concepts discovered from a set of data.

My problem is that sometimes I need just to instantiate one concept of the ontology. And I'm confused since in Jena, we need a complete Statement to instantiate an ontology.

Assuming that I've the following ontology.

enter image description here

What would be the statement to instantiate only one concept on the ontology for example EventType?

Is it necessary to have a Statement to instantiate an ontology ?

or Is my ontology not expressive enough ?

Edition : My Jena Code

public static void manageOntologies() throws FileNotFoundException{     

    int i,inFrame, lineSize;
    int frameNum = 0;

    Individual individu;
    Resource   resource;
    Statement  statement;
    OntModel   domainModel;

    Vector<String> lines = readFile("data/Trace.dat");

    String[] parts = null;
    String   event = null;

    domainModel = ModelFactory.createOntologyModel(ProfileRegistry.OWL_DL_LANG);
    domainModel.read((new FileInputStream(ontopath)), null);

    lineSize = lines.size(); 

    for(i = 0; i < lineSize; i++){
        parts = lines.elementAt(i).split(" ");
        event = parts[parts.length - 1];            
        resource = domainModel.createResource(xmlbase + "frame" + frameNum);//, domainModel.getOntClass(xmlbase + "Event"));
        domainModel.add(resource, RDF.type, domainModel.getOntClass("Event"));

    }

    System.out.println("Numbre de frame = " + frameNum);

    domainModel.write(System.out);
}

And here are is problem encountered

Exception in thread "main" java.lang.NullPointerException
    at com.hp.hpl.jena.rdf.model.impl.ModelCom.add(ModelCom.java:929)
    at soctrace.Intology.manageOntologies(Intology.java:87) -- domainModel.add(...)
    at soctrace.Intology.main(Intology.java:38)

Edition 2 : My OWL/XML Code

<?xml version="1.0"?>
<!DOCTYPE rdf:RDF [
    <!ENTITY xsd "http://www.w3.org/2001/XMLSchema#" >
    <!ENTITY rdfs "http://www.w3.org/2000/01/rdf-schema#" >
    <!ENTITY rdf "http://www.w3.org/1999/02/22-rdf-syntax-ns#" >
    <!ENTITY tima "http://www.soctrace.org/ontologies/tima.owl#" >
]>


<rdf:RDF xmlns="http://www.w3.org/2002/07/owl#"
     xml:base="http://www.w3.org/2002/07/owl"
     xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#"
     xmlns:tima="http://www.soctrace.org/ontologies/tima.owl#"
     xmlns:xsd="http://www.w3.org/2001/XMLSchema#"
     xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
    <Ontology rdf:about="http://www.soctrace.org/ontologies/tima.owl">       
</Ontology>


<!-- http://www.soctrace.org/ontologies/tima.owl#Event -->

<Class rdf:about="&tima;Event">
    <rdfs:subClassOf rdf:resource="http://www.w3.org/2002/07/owl#Thing"/>
</Class>



<!-- http://www.soctrace.org/ontologies/tima.owl#EventDuration -->

<Class rdf:about="&tima;EventDuration">
    <rdfs:subClassOf rdf:resource="&tima;ValuePartition"/>
</Class>



<!-- http://www.soctrace.org/ontologies/tima.owl#EventType -->

<Class rdf:about="&tima;EventType">
    <rdfs:subClassOf rdf:resource="&tima;ValuePartition"/>
</Class>



<!-- http://www.soctrace.org/ontologies/tima.owl#ValuePartition -->

    <Class rdf:about="&tima;ValuePartition"/>
</rdf:RDF>

Thanks for any reply !

Upvotes: 1

Views: 1404

Answers (2)

Ian Dickinson
Ian Dickinson

Reputation: 13315

It's hard to be precise, since you haven't provided your data or ontology (so we can't try your code). However, it is quite likely that this is the problem:

domainModel.getOntClass("Event")

"Event" is not a URI, so it is very unlikely that your ontology has an event class by that name (and if it does, you should change it to use full URI's instead!).

You will need to provide a full URI to getOntClass, otherwise it will return null because it does not recognise the class. Assuming you provide a suitable value for EVENT_NS, then:

domainModel.getOntClass( EVENT_NS + "Event")

Upvotes: 2

user205512
user205512

Reputation: 8908

You are correct that in RDF you store statements, not individual terms or concepts. However everything has a type, even if it's just rdfs:Resource (or in owl typically owl:Individual or owl:Class). Thus you all always add something via a statement of the form thing rdf:type Type, just pick the appropriate type.

In this case presumably EventType is a class? In that case:

Resource eventTypeResource = model.createResource(eventTypeURI);
model.add(eventTypeResource, RDF.type, OWL.class);

However that's such a common pattern you can use:

Resource eventTypeResource = model.createResource(eventTypeURI, OWL.class);

Or even better use the Jena ontology API:

OntClass eventTypeResource = ontModel.createClass(eventTypeURI);

(OntClass is still a Resource, but with some very useful methods added)

Jena provides a nice introduction to the ontology api.

Upvotes: 2

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