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

From: Jim Hendler <hendler@cs.rpi.edu>
Date: Wed, 13 Aug 2008 12:00:45 -0400
Cc: "Ian Horrocks" <ian.horrocks@comlab.ox.ac.uk>, "Ivan Herman" <ivan@w3.org>, <public-owl-wg@w3.org>, "Alan Wu" <alan.wu@oracle.com>
Message-Id: <7C1B67DD-56E5-4D3D-B516-BAA08EA01419@cs.rpi.edu>
To: Michael Schneider <schneid@fzi.de>

Between Michael's email, and some off list clarifications - it seems  
to me the discussion seems to be primarily with respect to  
completeness, not soundness - is this right?  If so, I'd point out  
that in OWL 1.0 we were very careful not to define completeness as a  
criterion (in part because know one knew at the time how to correctly  
combine nominals and inverse in the presence of the UNA - and thus in  
a certain sense none of the early OWL reasoners was actually complete)  
-- seems to me that for OWL RL, soundness is easy to define and we  
might simply stop there - I am actually not sure at this point if that  
is exactly what Boris was suggesting or exactly the opposite, but  
maybe this is one of those times when saying less is better (and the  
market will winnow out any implementations that are sound but trivial)
  -JH



On Aug 13, 2008, at 5:10 AM, Michael Schneider wrote:

> 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)
> Tel  : +49-721-9654-726
> Fax  : +49-721-9654-727
> Email: Michael.Schneider@fzi.de
> Web  : http://www.fzi.de/ipe/eng/mitarbeiter.php?id=555
>
> FZI Forschungszentrum Informatik an der Universität Karlsruhe
> Haid-und-Neu-Str. 10-14, D-76131 Karlsruhe
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>

"If we knew what we were doing, it wouldn't be called research, would  
it?." - Albert Einstein

Prof James Hendler				http://www.cs.rpi.edu/~hendler
Tetherless World Constellation Chair
Computer Science Dept
Rensselaer Polytechnic Institute, Troy NY 12180
Received on Wednesday, 13 August 2008 16:02:25 GMT

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