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I'm trying to check an ontology for its consistency. The ontology includes only descriptions of individuals, the class and semantic rules are described by an imported ontology.

I thougt using the isConsistenct method would be the right choice.

OWLReasonerFactory reasonerFactory = new StructuralReasonerFactory();
OWLReasoner reasoner =     reasonerFactory.createNonBufferingReasoner(mergedOntology);
    if(reasoner.isConsistent()){
        return "Merged ontology PASSED the consistency test";
    }else{
        return "Ontology FAILED the consistency test";
    }

What would be the correct approach to check the ontology's consistency, like Protege 5 applies when starting a reasoner?

Code update using Pellet

        OWLReasonerFactory reasonerFactory = new PelletReasonerFactory();
        OWLReasoner reasoner = reasonerFactory.createNonBufferingReasoner(mergedOntology);
        String answer = "";
        if(reasoner.isConsistent()){
            if(reasoner.getUnsatisfiableClasses().getEntitiesMinusBottom().size()>0){
                answer = "Merged ontology FAILED satisfiability test. Unsatisfiable classes detected: " + reasoner.getUnsatisfiableClasses().getEntitiesMinusBottom().size();
            }
            answer = "Merged ontology PASSED the consistency test";
        }else{
            answer = "Merged ontology FAILED the consistency test, please review the Axioms or debug using Protege";
            //FYI an example how to implement a working debugger can be found on sourceforge's OWL API page under Debugger 
        }
        reasoner.dispose();
        return answer;
Corpswalker
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  • What is the question exactly? You can calculate the inconsistency with this method. If you want to get the unsatisfiable classes you need to use another method. – Artemis Jun 17 '15 at 13:27

2 Answers2

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The approach is right but the use of the StructuralReasonerFactory is an issue. That reasoner does no real reasoning, it merely uses asserted axioms to answer some basic queries. It cannot check consistency.

You need to use a real reasoner to carry out the consistency check. There are a few reasoners already supporting OWLAPI 4, see https://github.com/owlcs/owlapi/wiki

Ignazio
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  • Thanks, I tried using Pellet as reasoner. Inconsistent ontologies are detected now, but I'm not sure if I need to check every class for its satisfiability in order to be safe about the ontology's soundness. – Corpswalker Jun 21 '15 at 20:31
  • Some classes can be unsatisfiable by design, although that's not a common occurrence. Their presence doesn't make the ontology unsound, although it might raise questions. Whether that's ok depends on the specific ontology. – Ignazio Jun 21 '15 at 22:33
  • Is the use of the "reasoner.getUnsatisfiableClasses().getEntitiesMinusBottom()" method call the right approach to check if there are any unsatisfiabilities? – Corpswalker Jun 22 '15 at 09:10
  • Yes that's correct. getEntitiesMinusBottom is a convenience so you can just check if it's empty to see if any unsatisfiable classes exist. – Ignazio Jun 22 '15 at 09:27
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Protege is also using some sort of isConsistent method. Depending on which version you are referring to, this method either is built in by the developers or used the one that is developed in OWL API. For example, look at this. However, when you run the reasoner in Protege, both the inConsistent and isSatisfiable methods are fired. So what you see is the result of two actions. Read the following blog post for understanding the difference if you need. The gist is:

So, while we can have unsatisfiable classes in a consistent ontology, all classes in an inconsistent ontology are unsatisfiable because an inconsistent ontology simply has no model, and thus it can’t have one with instances of any given class.

If you want to find the unsatisfiable classes, you just need to call the isSatisfiable method on all the classes:

reasoner.isSatisfiable(className);
Artemis
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  • Is there a need for calling the isSatisfiable method if the reasoner doesn't detect an inconsistency? – Corpswalker Jun 21 '15 at 20:28
  • Yes, there is a need. As mentioned above, an ontology can be consistent, but have unsatisfiable classes. Normally when you are working with the A-Box, inconsistency is more likely to arise, and when you are working with T-Box, unsatisfiability will occur. – Artemis Jun 22 '15 at 07:02
  • Thanks for your answer. The ontologies to be checked are only A-Box type. Just individuals. – Corpswalker Jun 22 '15 at 09:08