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Re: thoughts on the new rdfs:subClassOf

From: pat hayes <phayes@ai.uwf.edu>
Date: Wed, 29 Aug 2001 15:12:38 -0700
Message-Id: <v0421010ab7b316386dfa@[130.107.66.237]>
To: "Peter F. Patel-Schneider" <pfps@research.bell-labs.com>
Cc: joint-committee@daml.org, w3c-rdfcore-wg@w3.org
>Here are some thoughts on rdfs:subClassOf.
>
>peter
>
>
>	Notes on the new definition of rdfs:subClassOf
>
>The RDF Core working group has modified the definition of rdfs:subClassOf
>to indicate that rdfs:subClassOf means proper subclass.  ....

NO, what I sent you was a DRAFT which has not been formally 
considered by the WG yet, let alone approved by them. You saw it 
first. The WG hasnt 'done' anything about this issue yet, so please 
don't say that it has.

>This is a consequence of Pat Hayes's model theory, and need not be true in
>other definitions that make rdfs:subClassOf be a proper subclass.

Quite.  All blame is mine so far, and your points (especially point 
1)  have firmly convinced me that the WG should definitely NOT modify 
this definition, so please don't tell anyone else that it has done, 
there's a good chap.

And thanks for the input, most valuable.

Pat

PS.

>2/ If A is an rdfs:subClassOf of B then B has at least one member in every
>model.  This means that B cannot even be contingently empty.  Thus
>from
>        <daml:Class rdf:ID="Confused">
>	</daml:Class>
>	<daml:Class rdf:ID="SubConfused">
>	  <rdfs:subClassOf rdf:resource="#Confused">
>	</daml:Class>
>it follows that Confused has cardinality at least one.  Again, it is
>strange that simply having a subclass provides a minimum cardinality for a
>class.

Well, this seems perfectly natural to me. In fact the analogous 
assumption for 'parts' is considered one of the basic axioms of 
mereology, often called the proper part axiom: if A is a part of B, 
then there must be some other part C of B which is separate from A. 
Denying this axiom leads to models where everything has infinite 
descending chains of 'parts' all of which are extensionally 
indistinguishable. It also seems to be the intuitive basis for the 
fact that the empty set has no proper subsets.

But never mind, (1) was enough.

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Received on Wednesday, 29 August 2001 18:11:31 EDT

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