[protege-discussion] Exception in inference api

[Timothy Redmond]

The types of questions you have been  asking are better asked on the p4 
mailing list as it is about the Protege 4 owl editor.  Instructions for 
joining that list are here:

    http://mailman.stanford.edu/mailman/listinfo/p4-feedback
       


I used your code pretty much verbatim and did not see the null pointer 
exception.  In fact the code pretty much did what I expected.  I think 
that this issue can be cleared up if you supply a bit more information.

> but I have an exception in this line: 
> ontologygenerator.fillOntology(ontologymanager,ontology);
> this exception says: java.lang.NullPointerException
>  I don't know what i should do and what is wrong.

I suspect that we would know what is wrong immediately if we saw the 
exception stack trace.  A null pointer that actually thown on that line 
would seem to be impossible with the code you sent (based on Java 
principles only).  The only way to get the null pointer on that line is 
if the ontologygenerator variable is null but it is assigned to a 
constructed value in the previous line.

So I think that your exception is generated somewhere in code called by 
the line

    ontologygenerator.fillOntology(ontologymanager,ontology).


Somewhere down inside there something has not been initialized 
correctly.  An obvious guess is that things went wrong because the

    OWLOntology ontology=ontologymanager.loadOntology(IRI.create(OwlUri));


line did not successfully load an ontology.  But I (accidentally 
actually) tested that and it results in an exception at that line.  So I 
would guess that this is not the issue either.

I have some other immediate comments on your code.

> I used protege 4.1 beta build 209 api, and I have a problem in 
> inference api.

All the code you have supplied is actually based on the Manchester OWL 
API (owlapi.sourceforge.net) which is an important library used by 
Protege 4.1. I didn't see any Protege specific code in your sample.


In this code there is the line:

    OWLReasonerFactory reasonerfactory= new Reasoner.ReasonerFactory();


If you are planning on using this code in Protege 4.1 then this is not 
the recommended approach.  But your approach may be best for making 
quick little applications that you can test before integrating with 
Protege 4.1. A better approach if you integrate your code into Protege 
4.1 would be something like

    OWLReasoner owlreasoner = getOWLModelManager().getReasoner();
    if (owlreasoner instanceof NoOpReasoner) {
         ... tell the user to initialize his reasoner ...
         return;
    }
    else if (!owlreasoner.getPendingChanges().isEmpty()) {
         owlreasoner.flush();
    }
       


Most plugin types (view components, menus) will have a 
getOWLModelManager() method. I add the reasoner.flush() call here 
because I figure that an export inferred axioms operation is 
sufficiently expensive that it makes sense to bring the reasoner up to 
date first.

Then later you do this step:

    owlreasoner.precomputeInferences(InferenceType.CLASS_HIERARCHY);


It is a good idea to do the precompute step here but you chose the wrong 
one for the task that follows.  When you create the 
InferredOntologyGenerator, you tell it to compute inferred class 
assertion axioms (e.g. statements that an individual is in a class).  
Precomputing the class hierarchy will not help with this task.

-Timothy



On 10/10/2010 07:06 AM, Soha Said wrote:
> I used protege 4.1 beta build 209 api, and I have a problem in 
> inference api.
> This is the snapshot of code that I used to get inferencing:
> OWLOntologyManager ontologymanager=OWLManager.createOWLOntologyManager();
>             OWLOntology 
> ontology=ontologymanager.loadOntology(IRI.create(OwlUri));
>             OWLDataFactory factory=ontologymanager.getOWLDataFactory();
>             OWLReasonerFactory reasonerfactory= new 
> Reasoner.ReasonerFactory();
>             OWLReasoner 
> owlreasoner=reasonerfactory.createNonBufferingReasoner(ontology);
>             
> owlreasoner.precomputeInferences(InferenceType.CLASS_HIERARCHY);
>
> List<InferredAxiomGenerator<? extends OWLAxiom>> InferredGenerator = 
> new ArrayList<InferredAxiomGenerator<? extends OWLAxiom>>();
>            InferredGenerator.add(new 
> InferredClassAssertionAxiomGenerator());
>            InferredOntologyGenerator ontologygenerator=new 
> InferredOntologyGenerator(owlreasoner,InferredGenerator);
>            ontologygenerator.fillOntology(ontologymanager,ontology);
>            ontologymanager.saveOntology(ontology,IRI.create(OwlUri));
> but I have an exception in this line: 
> ontologygenerator.fillOntology(ontologymanager,ontology);
> this exception says: java.lang.NullPointerException
>  I don't know what i should do and what is wrong.
> Thanks in advance
> Soha Said
>
>
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