Is it possible to find out whether two instances are of the same RDF class, programmatically?

Question

Is it possible to find out whether two instances are of the same class, programmatically (Using api such as JENA)

Quirites

Can you use pure Java methods? – Sec

Why Jena? You can easily get the .class of the two objects and compare them. – Dayton

I don't think the question concerns java instances and classes, but RDF / OWL instances and classes. – Clareclarence

user205512: you are right, I would like to compare RDF/OWL instances. – Quirites

Answer 1

Easy in SPARQL:

ASK { <instance1> a ?class . <instance2> a ?class . }

In Jena API:

boolean shareClass = false;
for (Statement s: instance1.listProperties(RDF.type)) {
    if (instance2.hasProperty(RDF.type, s.getObject()) {
        shareClass = true;
        break;
    }
}

Not very elegant.

Clareclarence

Now that SPARQL 1.1 has property paths, the SPARQL query simplifies to ASK { ?class ^a <instance1>, <instance2> }. It captures very well "is there a class of which both instance1 and instance2 are instances?" – Bordelon

Answer 2

Assuming you are using the Jena ontology API, it's pretty straightforward. Note that in RDF, a given instance can have many types, so your question is really "how can I test if two instances have one or more types in common?".

I would do it as follows. Assume the two instances you want to test are Individual objects (note that you can do this with OntResource, or even Resource with a slight change in the code):

Individual i0 = ....;
Individual i1 = ....;

List the rdf:type values for each, and convert them to sets

Set<Resource> types0 = i0.listRDFTypes( false ).toSet();
Set<Resource> types1 = i1.listRDFTypes( false ).toSet();

They have types in common if the intersection is non-empty:

types0.retainAll( types1 );
if (!types0.isEmpty()) {
    // at least one type in common
    // types0 contains the common type resources
}

Dissogeny

That is more pleasant. Guava has Sets.intersection which would be even more readable. Typo: ...types1 = i1.listRDFTypes... – Clareclarence

Hi, I still have some confusion. Hope you can clear that out. As you suggested I get the types and compare their intersection. The problem is: for instances of two different classes the listRDFTypes still returns [http://www.w3.org/2002/07/owl#Class] as a type. As a result, any two instances I take are of same type. Am I missing something? – Quirites

If a resource has rdf:type owl:Class, it is a class not an instance of a class. Or there's something unusual or broken in your modelling. If you are convinced that having rdf:type owl:Class is correct for your domain model, then you could filter out owl:Class from the set. If this isn't enough of an explanation, please prepare a minimal example of the problem (code and data) and email it to the jena-users support list at Apache. – Dissogeny

Answer 3

Compare their classes:

boolean same = obj1.getClass().equals(obj2.getClass());

Thorianite

The OP was not 100% clear about this, but the question most likely concerns RDF/OWL classes and instances, not Java class comparison. – Metastasis

Answer 4

I take it this is an extension to your earlier post so

if (resource1.hasProperty(model.createProperty("http://www.w3.org/1999/02/22-rdf-syntax-ns#", "type"), model.createResource("http://typeUri")) && resource2.hasProperty(model.createProperty("http://www.w3.org/1999/02/22-rdf-syntax-ns#", "type"), model.createResource("http://typeUri"))) {
    // both resources are the same type
}

Enarthrosis