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Re: [OWLWG-COMMENT] Punning and the "properties for classes" use case

From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
Date: Sun, 04 Nov 2007 08:30:50 -0500 (EST)
Message-Id: <20071104.083050.67898359.pfps@research.bell-labs.com>
To: schneid@fzi.de
Cc: evren@clarkparsia.com, public-owl-dev@w3.org

From: "Michael Schneider" <schneid@fzi.de>
Subject: RE: [OWLWG-COMMENT] Punning and the "properties for classes" use case
Date: Fri, 2 Nov 2007 20:23:14 +0100

> Hi, Evren!
> Evren Sirin wrote on November 02, 2007:
> >Michael,
> >You are correct in your understanding of punning. It is true that 
> >punning semantics is strictly weaker than OWL-Full semantics and the 
> >inferences you will get will be a subset of OWL Full entailments. But 
> >what is the alternative? Without punning, any ontology where 
> >classes are 
> >used as instances will not be allowed in OWL-DL and rejected by OWL-DL 
> >reasoners. So you have to use an OWL-Full reasoner which means you are 
> >stuck with incompleteness (I'm not aware of any OWL-Full reasoner) and 
> >depending on which OWL-Full reasoner you use incompleteness come from 
> >different parts (e.g. some reasoners doesn't support 
> >owl:sameValuesFrom, 
> >others don't support owl:oneOf, etc.). At least with punning you know 
> >what causes the incompleteness. 
> If metamodelling brings us away from decidability (this is the real problem,
> right?), then I see two alternatives:
>   (1) Stop hunting for metamodelling capabilities in OWL-1.1-DL.
>       Metamodelling, even in a restricted form, would really be 
>       a useful feature, but the community has already learnt 
>       to live with the current situation.
>   (2) Add general metamodelling (not necessarily complete OWL-Full support)
>       to OWL-1.1-DL, and remove the requirement for decidability.

Solution (2) gives up one
of the main features of OWL DL, namely decidability, so I don't see it
as a possibility.

> My personal preference would be to go the (1)-way for OWL-1.1-DL, as a fast,
> save and conservative solution. 

But why would one want to stay with (1) when there is a partial
solution that appears to have some support?  

> And then (later) start thinking about an
> additional language somewhere in the middle between OWL-1.1-DL and
> OWL-1.1-Full, which I would call "OWL-UseFull". ;-) This language would have
> a few additional most-wanted features (like metamodelling), but it does not
> allow you to build any of those scary (and useless) constructs, which you
> can actually build in OWL-Full.

Well one could certainly design a language that is OWL-DL or OWL 1.1
with some extra features, like RDF-style metamodelling (and what
else?).  Perhaps one could get tool builders (particularly of reasoning
systems) to support this language.  I don't think, however, that this is
within scope of the current WG, as it would require significant effort
on the part of reasoner builders, at a mininum.

> A caveat would be that decidability could then not be a requirement anymore.
> But I would not stop thinking about this proposal from the start on. One
> would have to determine if this brings real problems in /practice/. In fact,
> there is a lot of useful software around for undecidable problems, without
> getting into practical problems, as long as this software is used in a
> meaningful way (parser generators, type checkers for the Haskell language,
> automatic reasoners for FOL and HOL, computer algebra systems).

Yes, and some of them even work out well in practice, particularly type
checkers for SML and Haskell.  I don't think that you can include FOL
reasoners in this camp, as they still have to be babied along, even
though great strides have been taken in this area.  Remember that a
reasoner for an ontology language is not solving "hard" problems, so you
can't expect it to work with day-to-day human oversight.  Instead, such
a reasoner is more like a utility and is expected to almost always do
its work silently and effectively.

> >I might be wrong but I'm not aware of 
> >anything other than sameAs-equivalentClass (and possibly 
> >equivalentProperty) relation that would cause the punning semantics 
> >incomplete w.r.t OWL-Full semantics.
> I think this alone already suffices, no need to look for more. :)

Well, there are many related sources of incompletenes, including
continent equality, which make reasoning in this area more difficult to
deal with.  (This is not to say that it is more difficult in the worst
case, just that it complicates effective reasoner design.)

> >I'd be interested in seeing if 
> >there is any other use case where punning semantics does not entail 
> >everything OWL-Full semantics does.
> >
> >FWIW, punning has been implemented in Pellet for years and I don't 
> >remember any of our users calling it "confusing" or "useless".
> That's interesting to hear, I did not know this. But has this also been a
> feature in Pellet which has been /applied/ by /many/ users for years? 
> >I believe 
> >it is more of a personal style choice to use punning (it might be 
> >confusing for some people but not others). I think it is a 
> >viable option 
> >for "properties for classes" use case (though I'd personally call it 
> >classes as instances use case)
> Yes, better. And in fact, the property discussion in my mail was a little
> bit redundant. Though my intended message was in effect that with punning it
> is easy to believe that one can assign a property to a class, while one
> actually assigns it to some equally named, but possibly completely different
> individual resource. Now, after Alan's answer, I am not certain anymore, if
> it is still possible that an individual can be different from an
> equally-named class. This is a core question to me.
> >because most of these use cases do not 
> >depend on sameAs-equivalentClass relation.
> I think that this relation is so fundamental, that you cannot really avoid
> to stumble over it ever and ever again. Perhaps, I will come up with other
> examples in the future, which demonstrate the /practical/ problems (but not
> before my headache produced by this topic has gone away again ;-)).

> >Cheers,
> >Evren
> Cheers,
> Michael

Received on Sunday, 4 November 2007 13:41:54 UTC

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