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Re: RDF Issue rdfs-subClassOf-a-Property

From: by way of <Michel.Klein@cs.vu.nl>
Date: Mon, 26 Aug 2002 12:11:36 -0400
Message-Id: <>
To: www-rdf-comments@w3.org

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Date: Mon, 26 Aug 2002 11:45:29 -0400 (EDT)
Message-ID: <3D6A4D99.1B64A3C1@cs.vu.nl>
From: Michel Klein <Michel.Klein@cs.vu.nl>
Organization: Vrije Universiteit - computer science
To: Brian McBride <bwm@hplb.hpl.hp.com>
CC: www-rdf-comments@w3.org, Jeen Broekstra <jbroeks@cs.vu.nl>

Brian McBride wrote:
 > [[[
 > Can an instance of the Property class have a subClassOf property? What does
 > this mean?
 > ]]]


 > The wording of the formal resolution is a bit bare, so let me add a few
 > words of explanation.  What this means is that a resource can be both a
 > class and a property.  If it is a Class, the resource has a class extension
 > which is the set of members of the class.  If it is a property, it has a
 > property extension which is the set of pairs related by the property.  If
 > it is both a class and a property, then it has both a class extension and a
 > property extension.  The distinction between a class and its extension, and
 > a property and its extension is a mathematical trick introduced to avoid
 > Russel's paradox when we allows classes to be members of themselves.  As
 > you see, I hope, it also works nicely to enable a resource to be both a
 > property and a class.
 > Please could you respond to this message, copying www-rdf-comments@w3.org
 > indicating whether this is an acceptable resolution of this issue.

Clearly, the issue that we raised has been solved by the decision of the
RDFCore WG, because we asked for a clarification of the meaning.

It looks as a reasonable solution. However, we have some concerns about the
effect this might have on tools: likely most of them will not expect that a
resource can be a Class and Property at the same time. On the other hand, this
is a situation that will probably not occur very often.

Regards, Michel.
(also on behalf of Jeen Broekstra)

Michel Klein            <><   | Faculty of Sciences
                               | Vrije Universiteit
phone:  +31 20 444 7782       | De Boelelaan 1081a, room U3.50
http://www.cs.vu.nl/~mcaklein | 1081 HV  Amsterdam, the Netherlands 
Received on Monday, 26 August 2002 12:11:48 UTC

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