[JENA-805] Graph#isIsomorphicWith should use semantic equivalence when comparing blank nodes

• Type: Bug
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: Jena 2.12.1
• Fix Version/s: Jena 2.13.0
• Component/s: Jena
• Assignee: Andy Seaborne
• Reporter: Chris Beer
• Created: 23/Oct/14 20:29
• Updated: 30/Oct/14 21:54
• Resolved: 28/Oct/14 15:03

Description

It appears that Graph#isIsomorphicWith appears to use syntactic equivalence when comparing blank nodes:

https://github.com/apache/jena/blob/master/jena-core/src/main/java/com/hp/hpl/jena/graph/impl/GraphMatcher.java#L27

It should probably use semantic equivalence instead, or, at the very least, respect the RDF 1.1 equivalence of plain literals and xsd:string-typed literals.

Here is an example that I believe should be considered isomorphic:

    @Test
    public void isomorphismShouldRespectPlainLiteralEquivalence() {

        // Without worrying about a blank node, isomorphism works fine:
        Model model1 = ModelFactory.createDefaultModel();
        model1.read(IOUtils.toInputStream("<info:x> <info:y> \"x\""), "", "TTL");
        Model model2 = ModelFactory.createDefaultModel();
        model2.read(IOUtils.toInputStream("<info:x> <info:y> \"x\"^^<http://www.w3.org/2001/XMLSchema#string>"), "", "TTL");
        assertTrue(model1.isIsomorphicWith(model2)); // WORKS

        // Now with a blank node:
        Model model3 = ModelFactory.createDefaultModel();
        model3.read(IOUtils.toInputStream("<info:x> <info:y> [ <info:z> \"x\" ]"), "", "TTL");
        Model model4 = ModelFactory.createDefaultModel();
        model4.read(IOUtils.toInputStream("<info:x> <info:y> [ <info:z> \"x\"^^<http://www.w3.org/2001/XMLSchema#string> ]"), "", "TTL");
        assertTrue(model3.isIsomorphicWith(model4)); // BROKEN
    }