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RDF Issue rdfs-subClassOf-a-Property

From: Brian McBride <bwm@hplb.hpl.hp.com>
Date: Mon, 19 Aug 2002 16:14:27 +0100
Message-Id: <5.1.0.14.0.20020819160743.0225c9c8@0-mail-1.hpl.hp.com>
To: mcaklein@cs.vu.nl
Cc: www-rdf-comments@w3.org

Michel,

In

    http://lists.w3.org/Archives/Public/www-rdf-comments/2000AprJun/0045.html

you raised an issue which was captured in

   http://www.w3.org/2000/03/rdf-tracking/#rdfs-subClassOf-a-Property

as

[[[
Can an instance of the Property class have a subClassOf property? What does 
this mean?
]]]

As recorded in

   http://lists.w3.org/Archives/Public/w3c-rdfcore-wg/2002Apr/0406.html

the RDFCore WG has resolved:

[[

   o an instance of the Property class may have an rdfs:subClassOf
     property

   o the meaning of such a property is defined by the model theory

   o this issue be closed
]]

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.

Brian McBride
RDFCore co-chair
Received on Monday, 19 August 2002 11:15:59 GMT

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