W3C home > Mailing lists > Public > www-webont-wg@w3.org > January 2003

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

From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
Date: Fri, 03 Jan 2003 06:49:19 -0500 (EST)
Message-Id: <20030103.064919.98599063.pfps@research.bell-labs.com>
To: connolly@w3.org
Cc: hendler@cs.umd.edu, ziv@unicorn.com, heflin@cse.lehigh.edu, 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 00:09:16 -0600

> On Thu, 2003-01-02 at 20:14, Jim Hendler wrote:
> > At 18:44 -0600 1/2/03, Dan Connolly wrote:
> > >On Thu, 2003-01-02 at 17:12, Jim Hendler wrote:

[...]

> > As I read the semantics document, the class defined as "all people 
> > who are students and classmembers" is a different class than "all 
> > people who are students" even if we assert that
> >   :classmember owl:sameClassAs owl:nothing.
> > which would mean they necessarily have the same membership.  (because 
> > the restrictions and assertions associated with the class are 
> > different)
> > 
> > Am I correct?

No, but only because your example doesn't work the way you want it to.


In OWL, you can even have the following situation

_:x rdf:type owl:Class .
_:x owl:onProperty ex:foo .
_:x owl:allValuesFrom ex:bar .

_:y rdf:type owl:Class .
_:y owl:onProperty ex:foo .
_:y owl:allValuesFrom ex:bar .

> Not if they're owl classes; if they're owl classes, and they
> have the same extension, then they're identical.

Any interpretation of the above six triples necessarily has the resources
that are the denotation of _:x and _:y having the same class extension.
However, there is no requirement in OWL that _:x and _:y denote the same
resource.

> Hmm... double-checking current draft...
> http://www-db.research.bell-labs.com/user/pfps/owl/semantics/rdfs.html#5.2
> 
> I don't see the constraint that IOT, IOC, and LV are
> mutually disjoint. We talked about that in a telcon, no?

This constraint is not in Section 5.2 because Section 5.2, as is stated in
its first paragraph, is about the similarities between interpretations for
OWL/DL and OWL/Full.  In Section 5.3, there is the domain-separation
constraint for OWL/DL.  OWL/Full does not have this domain-separation
constraint.

> 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.

> Hmm... I don't actually see the constraint that
> if two classes have the same extension then they're
> identical, 

FINALLY!  Then why have you been arguing that it exists?

> but I also don't see anything that
> conflicts with adding it.

Of course you don't.  There is nothing (that I can think of) that would
cause a semantic extension of OWL to be trivial if (a version of) this
semantic constraint was added.  This doesn't mean that it is a reasonable
thing to do for OWL, however.  There are lots of semantic constraints that
could be added to the OWL model theory that don't cause problems but that
nevertheless are not in the model theory.

> Dan Connolly, W3C http://www.w3.org/People/Connolly/

peter
Received on Friday, 3 January 2003 06:49:49 GMT

This archive was generated by hypermail 2.2.0+W3C-0.50 : Monday, 7 December 2009 10:57:56 GMT