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Re: rdfs:subClassOf and metaclasses

From: Brian McBride <bwm@hplb.hpl.hp.com>
Date: Wed, 03 Jul 2002 08:37:57 +0100
Message-Id: <>
To: Piotr Kaminski <piotr@ideanest.com>, www-rdf-comments@w3.org

At 17:48 02/07/2002 -0700, Piotr Kaminski wrote:

> > >3.  Introduce a rule into RDFS prohibiting the situation above:
> >
> > My take is that this going beyond what RDFS is trying to do.  Others may
> > disagree.  Danbri, Guha?
>I am now convinced that this is a real problem in RDFS.

In that case, maybe one of the schema editors could take over this thread.

The first step in this process is to establish exactly what the problem 
is.  The only "problem" I see below is that you don't think the current 
proposal "makes sense".  We need something a little stronger than that, 
e.g. an internal contradiction.

>   The rdfs:subClassOf
>property already restricts its domain and range to rdfs:Class, because
>subclassing only "makes sense" for classes.  But what happens when (for
>whatever reason) you have different kinds of classes, i.e. different
>subclasses of rdfs:Class?  I think subclassing only "makes sense" for
>classes instantiated from the same metaclass [1].  (This can be relaxed to
>"related metaclasses", with the relationship as explained below.)

So let me offer you a counter example:

Consider www to be a subclass of xxx, that www is of type B, the class of 
resources defined by Brian, and xxx is of type P, the class of resources 
defined by Piotr.  Then applying your rule:

If E contains:
   www [rdfs:subClassOf] xxx
   www [rdf:type] yyy
   xxx [rdf:type] zzz
then add:
   yyy [rdfs:subClassOf] zzz

  www rdfs:subClassOf xxx
  www rdf:type        B
  xxx rdf:type        P
  B rdfs:subClassOf P

i.e. I conclude that the class of resources defined by Brian is a subClass 
of the resources defined by Piotr, i.e. every resource defined by Brian is 
also a resource defined by Piotr. That is not a valid inference.

Received on Wednesday, 3 July 2002 03:39:13 UTC

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