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Re: ISSUE: owl:Class name misleading; try owl:Set?

From: Dan Connolly <connolly@w3.org>
Date: 01 Jan 2003 16:43:20 -0600
To: "Peter F. "Patel-Schneider <pfps@research.bell-labs.com>
Cc: www-webont-wg@w3.org
Message-Id: <1041461000.19700.67.camel@dirk.dm93.org>

On Wed, 2003-01-01 at 15:59, Peter F. Patel-Schneider wrote:
> From: Dan Connolly <connolly@w3.org>
> Subject: ISSUE: owl:Class name misleading; try owl:Set?
> Date: 01 Jan 2003 14:25:21 -0600
> 
> > 
> > Based on some comments about sameClassAs
> > http://lists.w3.org/Archives/Public/public-webont-comments/2002Dec/0004.html
> > 
> > and chatting with a few people about the relationship
> > between rdfs:Class and owl:Class, I have come to
> > the conclusion that owl:Set would be a better name
> > for what we currently call owl:Class.
> 
> OWL classes do not act like sets.  They have an identity distinct from
> being a set of their instances.

I don't understand what you mean by that.

> > In RDFS, one can have two classes whose
> > members are {a,b,c}, but they can be distinct;
> > the one class might be rdfs:label'ed "first
> > three letters" and the other might e rdfs:label'ed
> > "my three favorite letters". RDFS classes have
> > properties other than their extension.
> > 
> > In DAML+OIL, if they have the same members, they're
> > the same class.
> 
> Incorrect.  Two distinct classes in DAML+OIL can have the same members.

For example?

I thought the DAML+OIL semantics said that classes that have
the same members are identical. In
  http://www.daml.org/2001/03/model-theoretic-semantics
IC maps names directly to sets of members. So two names
that denote the same set of members denote the same thing,
no?

> Two distinct classes in DAML+OIL can even necessarily have the same
> members.
> 
> > Gee, to me, that sounds like a set.
> 
> If it was correct, then DAML+OIL classes would be more like sets.
> 
> > In fact, I asked for terms for sets as soon as
> > I realized how rdfs:Class works:
> > 
> > vocabulary for traditional sets
> > From: Dan Connolly (connolly@w3.org)
> > Date: Tue, Nov 06 2001
> > http://lists.w3.org/Archives/Public/www-rdf-comments/2001OctDec/0210.html
> > 
> > We already use set-theoretic terms like
> > intersectionOf, unionOf...
> > so I think owl:Set is a better name for what
> > we call owl:Class. And owl:sameMembersAs
> > is probably better than owl:sameClassAs.
> 
> OWL classes are not sets, so owl:Set is not a good name for them.
> 
> owl:sameMember[s]As might be a better name for owl:sameClassAs.
> 
> > These should be theorems in full owl:
> > 
> > 	?X owl:sameMembersAs ?Y
> > 	<==>
> > 	?X rdfs:subClassOf ?Y.
> > 	?Y rdfs:subClassOf ?X.
> 
> This is now true for owl:sameClassAs
> 
> > and
> > 
> > 	?X rdf:type owl:Set.
> > 	?Y rdf:type owl:Set.
> > 	?X owl:sameMembersAs ?Y.
> > 	==>
> > 	?X owl:sameAs ?Y.
> 
> This is not true in OWL.

No? Hmm... I guess I read the semantics document
too fast.

Jeremy/Jos, please add that to the test suite, regardless
of whether it turns out to be an entailment test
or a non-entailment test.

> > (we did rename equivalentTo to sameAs, didn't we?
> > I should look that up...)
> > 
> > I suppose this is a new issue; I don't think I could
> > argue that it's an editorial fix. Sorry I didn't
> > get it in sooner.
> 
> I'm not sure what you are proposing here.  It seems to me that you are
> either saying that OWL classes already act like sets, which is incorrect,

I don't understand how it's incorrect. Please explain.

> and thus that various names should be changed, or that OWL classes should
> act like sets, which I would oppose.

Why?

> > Dan Connolly, W3C http://www.w3.org/People/Connolly/
> 
> 
> peter
-- 
Dan Connolly, W3C http://www.w3.org/People/Connolly/
Received on Wednesday, 1 January 2003 17:43:08 GMT

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