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

From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
Date: Fri, 03 Jan 2003 10:58:11 -0500 (EST)
Message-Id: <20030103.105811.104771860.pfps@research.bell-labs.com>
To: connolly@w3.org
Cc: www-webont-wg@w3.org

From: Dan Connolly <connolly@w3.org>
Subject: Re: ISSUE: owl:Class name misleading; try owl:Set?
Date: 03 Jan 2003 09:12:14 -0600

> On Fri, 2003-01-03 at 05:49, Peter F. Patel-Schneider wrote:
> > > In fact, I asked that it be added to the owl schema:
> > > 	owl:Thing owl:disjointFrom owl:Class.
> > > 	owl:Thing owl:disjointFrom rdfs:Literal.
> > > 	owl:Class owl:disjointFrom rdfs:Literal.
> > > and I thought Mike or Pat said they'd do it... or at
> > > least think about it.
> > 
> > This prevents classes from being instances in OWL/Full.
> It prevents owl:Classes from being owl:Things;
> It doesn't prevent owl:Classes from being rdf:Resources
> nor does it prevent rdfs:Classes from being rdf:Resources.

Correct, I was being sloppy.  

> This is by design, no? Perhaps that's not the way other
> folks understood the design, but that's what I had in mind when we
> closed the layering issue.

OWL/Full does not have this situation.  In fact, it is not possible in
OWL/Full, as 
1/ OWL/Full identifies the class extensions of owl:Thing and rdfs:Resource
   (see Section 5.4 of AS&S);
2/ rdfs:Literal is a subset of the class extension of rdfs:Resource
   (because the class extension of rdfs:Resource is the entire universe,
   from Section 3.3 of RDF Semantics);
3/ rdfs:Literal is non-empty because it contains all the untyped literals,
   including all strings.

OOPS: Point 3 is not (no longer?) true!!!  There are NO semantic
constraints on rdfs:Literal except that it denote a class (and be the range
of rdfs:comment and rdfs:label).  In fact rdfs:Literal appears to be
completely broken.  I'm composing a message to www-rdf-comments on this
that I will copy to www-webont-wg.

> In any case, that's what I'm proposing now.

This would go against the design of OWL/Full.  


[Now talking about making OWL classes much more similar to sets.]

> That it's a reasonable thing to do doesn't follow as a logical
> necessity from the fact that it's technically possible, no.
> But I think it is a reasonable and useful thing to do, for
> other reasons. OWL introduces terminology such as
> intersectionOf and unionOf. As was pointed out when
> I presented some early model theory proposals, the
> traditional usage of "intersection" has exactly
> *one* intersection of any classes C1, C2, C3, ... CN.
> i.e.
> 	?I1 owl:intersectionOf (:C1 :C2 :C3).
> 	?I2 owl:intersectionOf (:C1 :C2 :C3).
> 	==>
> 	?I1 owl:sameAs ?I2.

Well, it is the case that intersection is an functional constructor of
sets, but this doesn't mean that the intersection of classes need work the
same way.


Received on Friday, 3 January 2003 10:58:23 UTC

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