RE: ISSUE 131 (OWL R Unification): Different semantics on syntactic fragment

Hi Ian!

Ian Horrocks wrote:

>However, my hope and expectation is that conformance for OWL RL will
>be defined such that a reasoner is conformant if it is sound w.r.t.
>the OWL Full/RDF semantics, and is complete w.r.t. the entailments
>derived using the rule set. 

This statement starts to clarify things for me now. 

So soundness and completeness wouldn't be, as usual, specified w.r.t. a
*single* semantics, but there would be *two*: The ruleset for defining
completeness (the "lower bound" semantics), and OWL 2 Full semantics for
soundness (the "upper bound" semantics).

This would, of course, mean that there can be two different reasoners, which
happen to produce different sets of inferences for the same ontology, but
still, they can both call themselves be "compliant" rasoners. The only thing
which can be said in such a case is that the two sets of produced inferences
are both upper sets of the inferences expected from the ruleset. I wonder
whether this can lead to interop problems; others will have to tell me.

The question remains whether this completeness definition (w.r.t. the
ruleset) will hold for all RDF graphs, or is it restricted to ontologies
from the syntactic fragment only? If it holds for all RDF graphs, this would
mean that one cannot simply use a classic OWL DL reasoner for complete
reasoning in OWL RL. Instead, one has to make sure that such a reasoner is
also able to produce the necessary inferences for all of RDF. 

Technically, this would not be too hard to achieve: Just add a ruleset
reasoner, and delegate to it every RDF graph, which the syntax checker
detects to be not from the syntactic fragment of OWL RL (or at least not
valid OWL DL). 

>A reasoner of the kind you describe is
>trivially complete for entailments derived using the rule set, and
>also is trivially sound w.r.t. the OWL Full/RDF semantics; 

Yes.

>it would therefore be a conformant (compliant if you prefer) OWL RL
reasoner.

Ok. 

So to summarize, I still have two questions:

  * Does an OWL RL compliant reasoner need to produce the ruleset inferences
for every RDF graph, or only for ontologies from the syntactic fragment?
(Yes, I know, that's a conformance question. :))

  * Is it possible that this approach will lead to interop problems?

Cheers,
Michael

--
Dipl.-Inform. Michael Schneider
FZI Forschungszentrum Informatik Karlsruhe
Abtl. Information Process Engineering (IPE)
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