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Re: more on a same-syntax extension from RDF(S) to OWL

From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
Date: Tue, 05 Mar 2002 08:53:48 -0500
To: jos.deroo.jd@belgium.agfa.com
Cc: www-webont-wg@w3.org
Message-Id: <20020305085348O.pfps@research.bell-labs.com>
From: "Jos De_Roo" <jos.deroo.jd@belgium.agfa.com>
Subject: Re: more on a same-syntax extension from RDF(S) to OWL
Date: Tue, 5 Mar 2002 14:43:40 +0100

> 
> > > > I agree that http://www.agfa.com/w3c/euler/owl-rules.n3 does not
> sanction
> > > > any oneOf consequences.  Therefore, you will not get
> > > >    John a person .
> > > > to imply
> > > >         John a [ owl:oneOf ( John ) ].
> > > > from http://www.agfa.com/w3c/euler/owl-rules.n3.
> > > >
> > > > All this says, however, is that there are desirable inferences that
> > > > http://www.agfa.com/w3c/euler/owl-rules.n3 does not sanction, i.e.,
> > > > http://www.agfa.com/w3c/euler/owl-rules.n3 is incomplete.
> > >
> > > good point, I've added
> > >   { ?L owl:item ?x } log:implies { ?x a [ owl:oneOf ?L ] } .
> > > so now
> > >   the-empty-graph
> > > log:entails
> > >   :John a [ owl:oneOf ( :Frans :John :Mary ) ] .
> > > but that still doesn't give us an empty hypothesis to entail
> > >   _:1 owl:oneOf ( _:2 ) .
> > > I will think further...
> >
> > Actually it does, as this is (assuming I've got the _ and : in the right
> > order) a simple existential version of part of
> >
> > :John a [ owl:oneOf ( :John ) ]
> 
> But here it is written in the implied consequent graph
> so if one would have written the rule as
> { ?L owl:item ?x } log:implies { ?x a _:1 . _1 owl:oneOf ?L } .
> and normalize (eliminate existentials) that to following rules
> { ?L owl:item ?x } log:implies { ?x a [ :skf ?L, ?x ] } .
> { ?L owl:item ?x } log:implies { [ :skf ?L, ?x ] owl:oneOf ?L } .
> (using Skolem functional terms)
> then the _:c owl:oneOf ( _:r ) entailment follows,
> but we haven't written the rule like that...
> For ``facts'' such as :John a [ owl:oneOf ( :John ) ] .
> there is no problem to write them as
> :John a :skc . :skc [ owl:oneOf ( :John ) .
> (using Skolem constants) and we happen to also do that.
> Maybe we have confused the whole thing with [ ] notation
> but it is quite clear that one should not re-re-re-skolemize [ ]'s
> 
> --
> Jos


Well what I think that all this points out is the difficulty of writing
things in this way.  In particular, you have to be *very* careful how
you label what you are doing.

Note that you said that it doesn't *entail*, which is a semantic
relationship.  I pointed out that it does *entail*, which it does.  Your
rules won't infer it, as they are incomplete.

I think that it would be much better if everyone using N3 refrained from
using log:entails as the predicate in rule.  It would be even better if
they refrained from using log:implies, log:Truth, and other such properties
without pointing to a readable description of what they meant by such
properties.

Peter F. Patel-Schneider
Bell Labs Research
Received on Tuesday, 5 March 2002 08:55:45 GMT

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