I solved my question. I think there was a problem with my ontology. Therefore, I created another ontology to infer individuals. The ontology that I created contains Person and subclasses of Person : MalePerson, FemalePerson and MarriedPerson. And, there are two object properties(hasSpouse, hasSibling) and one data type property(hasAge).
And, I created 3 individuals.
John - MalePerson - hasAge(20) - hasSibling(Jane)
Jane - FemalePerson - hasSibling(John) - hasSpouse(Bob)
Bob - MalePerson - hasSpouse(Jane)
And, I put two restrictions for MalePerson and FemalePerson classes.
For MalePerson :
hasSpouse max 1
hasSpouse only MalePerson
For FemalePerson :
hasSpouse max 1
hasSpouse only FemalePerson
Lastly, I made MarriedPerson to be a defined class. Before reasoning, MarriedPerson has no individual. However, the model should infer that Jane and Bob are married. Therefore, at the end, MarriedPerson class should have 2 individuals.
When I ran this code in Java using Jena, I got 2 inferred individuals.
OntModel ontModel = ModelFactory.createOntologyModel();
InputStream in = FileManager.get().open(inputFileName);
if (in == null) {
throw new IllegalArgumentException( "File: " + inputFileName + " not found");
}
ontModel.read(in, "");
Reasoner reasoner = ReasonerRegistry.getOWLReasoner();
reasoner = reasoner.bindSchema(ontModel);
// Obtain standard OWL-DL spec and attach the Pellet reasoner
OntModelSpec ontModelSpec = OntModelSpec.OWL_DL_MEM;
ontModelSpec.setReasoner(reasoner);
// Create ontology model with reasoner support
OntModel model = ModelFactory.createOntologyModel(ontModelSpec, ontModel);
// MarriedPerson has no asserted instances
// However, if an inference engine is used, two of the three
// individuals in the example presented here will be
// recognized as MarriedPersons
//ns is the uri
OntClass marPerson = model.getOntClass(ns + "OWLClass_00000003866036241880"); // this is the uri for MarriedPerson class
ExtendedIterator married = marPerson.listInstances();
while(married.hasNext()) {
OntResource mp = (OntResource)married.next();
System.out.println(mp.getURI());
} // this code returns 2 individuals with the help of reasoner