[Rdfapi-php-interest] Inference at ontology level?

Hello,

I've begun using an InfModelF to add tripels to my model based on
subclasses defined in the ontology. This is a great help. If
   a subclass b
   b subclass c
   i type a
the model correctly infers that
   i type b
   i type c

I incorrectly assumed the model would also infer
   a subclass c

As I need the transitive closure of the subclass relation for the
purpose of querying the model, what I used to do is compute it myself
and store it in auxiliary files. I hoped the inference engine would save
me the trouble.

I have tried adding, in InfModel.php, in the function _addToInference, 
after case RDF_SCHEMA_URI.RDFS_SUBCLASSOF :

$infRule2=new InfRule();
$infRule2->setTrigger(null,new 
Resource(RDF_SCHEMA_URI.RDFS_SUBCLASSOF),$statement->getSubject());
$infRule2->setEntailment('<s>',new 
Resource(RDF_SCHEMA_URI.RDFS_SUBCLASSOF),$statement->getObject());
$this->infRules[]=$infRule2;		 
$this->_addInfRule($infRule2,$statementPosition);

$infRule3=new InfRule();
$infRule3->setTrigger($statement->getObject(),new 
Resource(RDF_SCHEMA_URI.RDFS_SUBCLASSOF),null);
$infRule3->setEntailment($statement->getSubject(),new 
Resource(RDF_SCHEMA_URI.RDFS_SUBCLASSOF),'<o>');
$this->infRules[]=$infRule3;
$this->_addInfRule($infRule3,$statementPosition);

which doesn't seem to work, and maybe I don't really know what I am 
doing here.

Anyone has an idea on how to get the kind of inference that I need?

Thanks,
Peter