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Re: Extensional interpretation of rdfs:subClassOf?

From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
Date: Mon, 12 Jan 2004 16:28:17 -0500 (EST)
Message-Id: <20040112.162817.98593794.pfps@research.bell-labs.com>
To: gk@ninebynine.org
Cc: w3c-rdfcore-wg@w3.org

From: Graham Klyne <gk@ninebynine.org>
Subject: Extensional interpretation of rdfs:subClassOf?
Date: Mon, 12 Jan 2004 13:18:24 +0000

> In message [1], Peter F. Patel-Schneider says:
> [[
> As far as the logic underlying OWL is concerned they are exactly the same.
>    :A rdfs:subClassOf :B
>    :B rdfs:subClassOf :A
> entails
>    :A owl:equivalentClass :B
> and
>    :A owl:equivalentClass :B
> entails
>    :A rdfs:subClassOf :B
>    :B rdfs:subClassOf :A
> ]]
> I understood that [OWL] classes were defined extensionally, and would 
> therefore expect that owl:equivalentClass was an extensional equivalence, 
> and that RDF classes are defined intensionally.

Well, not really.  Two OWL classes can have the same extension without
being the ``same'' class.  (At least for some definition of ``same''.)

> Does Owl strengthen the interpretation of rdfs:subClassOf?  

OWL does strengthen rdfs:subClassOf so that in an OWL interpretation if the
extension of A is a subset of the extension of B then A rdfs:subClassOf B.
See Section 5.2 of OWL S&AS for details.

> It seems that would be legitimate under the semantic extension regime set
> out in the semantics specification (True in RDF remains True in [OWL]),
> but I wonder about the wisdom (and potential for interoperability
> failure) if the interpretation of RDF core vocabulary can be modified by
> other specifications.

Well, just about any RDF graph modifies the interpretation of the RDF
core vocbulary.  For example the RDF graph that contains

	:A rdfs:subClassOf :B

modifies the interpretation of rdfs:subClassOf. 

> #g
> --
> [1] http://lists.w3.org/Archives/Public/www-rdf-logic/2004Jan/0030.html
> ------------
> Graham Klyne
> For email:
> http://www.ninebynine.org/#Contact

Peter F. Patel-Schneider
Bell Labs Research
Received on Monday, 12 January 2004 16:32:15 UTC

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