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Re: Dark triples motivation

From: Dan Connolly <connolly@w3.org>
Date: 16 Apr 2002 15:57:06 -0500
To: "Peter F. "Patel-Schneider <pfps@research.bell-labs.com>
Cc: Jeremy Carroll <jjc@hplb.hpl.hp.com>, www-webont-wg@w3.org
Message-Id: <1018990627.2382.6.camel@dirk>
On Tue, 2002-04-16 at 14:23, Peter F. Patel-Schneider wrote:
> From: Dan Connolly <connolly@w3.org>
> Subject: Re: Dark triples motivation
> Date: 15 Apr 2002 13:38:58 -0500
> 
> > On Mon, 2002-04-15 at 12:33, Peter F. Patel-Schneider wrote:
> > > The only problem that I see with your examples is that they concentrate on
> > > daml lists (daml:collection) and containers.  I see the problem much more
> > > as having to do with defined classes and restrictions, and lists and
> > > containers only showing up because they are needed in some places in
> > > defined classes and restrictions.
> > 
> > I'm still at a loss to see how 'dark triples' solves anything.
> > So I'd love to see an even simpler example of how it can help...
> > one that doesn't use lists/collections would be great.
> 
> Well, almost all the examples end up using daml lists, because so much
> of daml syntax uses daml lists.
> 
> Here is one of the really bad examples
> 
>    :_2, rdf:type, owl:Restriction .
>    :_2, owl:onProperty, rdf:type .
>    :_2, owl:maxCardinalityQ, "0" .
>    :_2, owl:hasClassQ, :_3 .
>       :_3, owl:oneOf, :_4 . 
>         :_4, owl:first, :_2 .
> 	:_4, owl:rest, owl:nil .
> 
> If you don't have dark triples, and you want to have reasonable
> inferences, then this kind of restriction ends up being in all owl
> interpretations.

I'm not quite sure of that, but suppose I stipulate to that for now;
that's an interesting-looking example...

>  As this restriction is self-contradictory, all owl
> interpretations contain a contradiction.
> 
> Why does this restriction have to be in all owl interpretations?  Well,
> because individuals can't belong to restrictions that don't exist.  Why is
> existence a characteristic of restrictions in the first place?  Well,
> because all triples are non-dark. 
> 
> So, dark triples will destroy this line of reasoning.

I'd like just a few more details at this point.

Please show me how you imagine applying dark triples to the example
above.

>  Is this a proof that
> they make all the semantic problems go away?  Of course not.  That requires
> an in-depth analysis of a proposal.  However, it appears to me that dark
> triples are sufficient to make these semantic problems go away.  Is this a
> proof that dark triples are needed to make all the semantic problems go
> away?  Of course not.  There are already proposals that do not have
> semantic problems and also do not need dark triples.  However, in my view,
> all these proposals have their own problems.  For example, RDFS is not
> expressive enough and DAML+OIL has far too weak entailment.
> 
> peter
-- 
Dan Connolly, W3C http://www.w3.org/People/Connolly/
Received on Tuesday, 16 April 2002 16:58:14 GMT

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