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RE: rdfs:class and rdfs:resource

From: Dieter Köhler <dieter.koehler@philo.de>
Date: Thu, 08 May 2003 12:07:52 +0200
Message-Id: <5.1.1.6.0.20030508113012.00ab0c90@pop3.philo.de>
To: www-rdf-interest@w3.org


>Thanks to everyone on attempting to clarify this rdfs:class and
>rdfs:resource issue. But, either I'm missing something, or these
>explanations are. Specifically, I need to see a careful description of the 
>classes and *instances* involved.

Perhaps things get clearer by concentrating on the essential statements 
about rdfs:Resource and rdfs:Class in the [RDF Schema] specification. In 
terms of the calculus specified in [RDF Schema] the following RDF 
statements are true (the numbers in brackets refer to the paragraph in the 
specification):

<rdfs:Resource> <rdf:type> <rdfs:Class> . (2.1)
<rdfs:Class> <rdf:type> <rdfs:Class> . (2.2)
<rdfs:Class> <rdfs:subClassOf> <rdfs:Resource> . (2.1)
<rdfs:Resource> <rdf:type> <rdfs:Resource> . (Because all instances of 
rdfs:Class are instances of rdfs:Resource, and rdfs:Resource is an instance 
of rdfs:Class (2.1 and 3.4).)

But the following is, as far as I can see, *not* true:
<rdfs:Resource> <rdfs:subClassOf> <rdfs:Class> .

In other words: There may exist instances of rdfs:Resources which are not 
instances of rdfs:Class.  Or again in other words: Not everything must be a 
class.

Footnote: I think it is unnecessary to talk *here* about 
meta-languages:  One may or may not on a meta-level require that all 
resources are classes (or in terms of scholastic philosophy: that all 
individuals are concepts).  And the question what comes first, resources or 
classes, might be interesting if we try to form a hierarchy of different 
calculuses based on each other, but the simple answer for [RDF Schema] is 
that it has no hierarchical structure and should be considered as a 
whole.  Of course one could try to reduce the number of its axioms while 
the possible conclusions remain the same, but because of the 
dissimilarities of rdfs:Resource and rdfs:Class neither can simply be 
reduced to the other.

Dieter Köhler

Institute of Philosophy
University of Karlsruhe
Germany
Received on Thursday, 8 May 2003 06:09:06 GMT

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