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Re: RDF Issue rdfs-clarify-subClass-and-instance

From: Graham Klyne <GK@ninebynine.org>
Date: Thu, 29 Aug 2002 23:19:48 +0100
Message-Id: <>
To: Nick Bassiliades <nbassili@csd.auth.gr>
Cc: www-rdf-comments@w3.org

At 01:17 PM 8/29/02 +0300, Nick Bassiliades wrote:

>I would like to ask if it legal to transform the following set of triples 
>that uses 2 rdf:type properties:
>A rdf:type rdfs:Class
>x rdf:type A
>x rdf:type rdfs:Class
>to the following set (which has just one rdf:type property):
>A rdf:type rdfs:Class
>A rdfs:subClassOf rdfs:Class
>x rdf:type A

I believe this is incorrect.

For a counter-example, consider that A is rdfs:Resource.

Then the first group of statements may be true for some value of x, but the 
second is clearly not true for any value of x (excepting the degenerate 
case of a universe of discourse that contains only rdfs:Class values).


Also, I note that your first group of statements is redundant:

   x rdf:type A


   A rdf:type rdfs:Class

so the same information would be conveyed by two statements:

   x rdf:type A
   x rdf:type rdfs:Class


>Actually, the first set of triples tries to say that A is a class of 
>classes. This (I believe)
>can be more elegantly said by the second set of triples.
>If the semantics of the 2 above are considered equivalent, then this 
>can be enforced to any meta-level of instantation, i.e. whenever a 
>resource is both
>an instance of its class and its class' class, then it can be made an 
>instance of only its class,
>by making its class a sub-class of its own class.
>I came up with this situation when looking at the DC namespace
>(especially the DC terms namespace http://purl.org/dc/terms/).
>* Dr. Nick Bassiliades                                       *
>*                                                            *
>* Programming Languages And Software Engineering (PLASE) Lab *
>* Logic Programming and Intelligent Systems (LPIS) Group     *
>*                                                            *
>* Dept. of Informatics, Aristotle University of Thessaloniki *
>* 54006 Thessaloniki, Greece                                 *
>*                                                            *
>* Tel: +30310998418    E-mail: nbassili@csd.auth.gr          *
>* Fax: +30310998419    URL:    http://www.csd.auth.gr/~nick  *

Graham Klyne
Received on Friday, 30 August 2002 08:11:46 UTC

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