[Pellet-users] getDeductionModel and updates by Jena OntModel prepare() : some questions

[Evren Sirin]

Yes, the deductionsGraph is set to null in the prepare function. I'm not 
sure what the problem you are seeing is but I would advise strongly not 
to use getDeductionsModel function whose behavior was changed in Pellet 
1.5.1 to return null. This is because the Jena javadoc describes this 
function as:

> getDeductionsModel
>
> Model getDeductionsModel()
>
>     Returns a derivations model. The rule reasoners typically create a 
> graph containing those triples added to the base graph due to rule 
> firings. In some applications it can useful to be able to access those 
> deductions directly, without seeing the raw data which triggered them. 
> In particular, this allows the forward rules to be used as if they 
> were rewrite transformation rules.
>
>     Returns:
>         the deductions model, if relevant for this class of inference 
> engine or null if not.
>

According to this description getDeductionsModel is not relevant for 
Pellet (which is obviously not a rule reasoner) and should have never 
been implemented. For this reason, the behavior in Pellet 1.5.1 has been 
changed to return null for this function with a temporary configuration 
option that gives the 1.4 behavior.  This configuration option will be 
removed in a future release so getDeductionsModel will always return 
null. If you continue using this function your code will break when you 
upgrade (which I strongly suggest because there have been many bug fixes 
since 1.4).

If what you want is to get the inferences Pellet computes then you can do

Model inferences = ModelFactory.createDefaultModel();
inferences.add( ontModel );
inferences.remove( ontModel.getRawModel() );


Cheers,
Evren


On 7/9/08 9:22 AM, Paolo Bussotti wrote:
> Hello everybody.
> I'm working with Pellet (1.4) through a Jena Pellet-backed OntModel,
> and I update the Knowledgebase by modifying the OntModel 
> and successively calling prepare() on it.
> I've seen that this corresponds to calling prepare() on the 
> PelletInfGraph that, if I'm not wrong, should set its deductionsGraph 
> variable
> to null, if some changes have happened (in this version, if the kb 
> have been reloaded).
> It all works fine, but when I try to get the deductionModel, calling 
> OntModel.getDeductionsModel, then, even after changes, the system 
> continues to give me back the same model. And this even if, after a 
> change, I've invoked prepare, therefore setting the variable 
> deductionsGraph to null: it looks like the variable deductionsGraph is 
> never set to null, and returns always the same model.
> Another question please: is it correct that the deduction model does 
> not modify the OntModel.BaseModel as iy happens instead with rule 
> reasoner ?
> I thank you all in advance.
> Best Regards
> Paolo Bussotti           
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