使用OWLAPi和JFact推理器获取特定类的所有个体

Question

Is there any way to get all individuals of a specific class using reasoner? Reasoner because i want to get all the inferred and assereted individuals of that class. I am using JFact reasoner, and i am trying for loops and if statement. And i want to find the individuals of class eg "person". But i am unable to see the individuals. Any idea about below code or is there any method for this purpose?

for (OWLClass c : myPizza.getClassesInSignature()) {
        NodeSet<OWLNamedIndividual> instances = reasoner.getInstances(c, true);
        System.out.println(c.getIRI().getFragment());
        if (c.getIRI().getFragment().equals("Person")){

            for (OWLNamedIndividual i : instances.getFlattened()) {
                System.out.println(i.getIRI().getFragment()); 

        }
    }
        else {
            continue;
        }
        break;

    }

Thanks

Answer 1

Calling reasoner.getInstances(c, true); will only give you the /direct/ instances of c; if the individuals you are after are instances of subclasses of c, they will be skipped. Switch to reasoner.getInstances(c, false); to include instances of subclasses.

You are also calling break; after the first iteration. If person is not the first class in the signature, you'll never look for instances of person .

You could slightly change your code to do less reasoning work:

for (OWLClass c : myPizza.getClassesInSignature()) {
    if (c.getIRI().getFragment().equals("Person")){
        NodeSet<OWLNamedIndividual> instances = reasoner.getInstances(c, false);
        System.out.println(c.getIRI().getFragment());
        for (OWLNamedIndividual i : instances.getFlattened()) {
            System.out.println(i.getIRI().getFragment()); 
        }
    }
}

Edit: Note from comments, if you expect to see SWRL inferred individuals you need to use a reasoner that supports SWRL, like Pellet or HermiT. JFact does not support SWRL rules.

Answer 2

Try out this method. You can get all individuals for a particular class using below method.

 private static void printIndividualsByclass(OWLOntology ontology, String owlClass){
    OWLReasonerFactory reasonerFactory = new PelletReasonerFactory();
    OWLReasoner reasoner = reasonerFactory.createNonBufferingReasoner(ontology);
    for (OWLClass c : ontology.getClassesInSignature()) {
        if (c.getIRI().getShortForm().equals(owlClass)){
            NodeSet<OWLNamedIndividual> instances = reasoner.getInstances(c, false);
            System.out.println("Class : "+ c.getIRI().getShortForm());
            for (OWLNamedIndividual i : instances.getFlattened()) {
                System.out.println(i.getIRI().getShortForm()); 
            }
        }
    }
}