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Re: [ANN] Working drafts by SW Best Practices group -- request for comments

From: Natasha Noy <noy@SMI.Stanford.EDU>
Date: Tue, 17 Aug 2004 10:10:15 -0700
Message-Id: <4EA8534E-F070-11D8-88D1-000A958B5C28@smi.stanford.edu>
Cc: public-swbp-wg@w3.org
To: Eric Jain <Eric.Jain@isb-sib.ch>

> Natasha Noy wrote:
>> There is nothing wrong with having classes in the hierarchy be 
>> instances of some metaclasses (in fact, i would argue very strongly 
>> that there are many cases where you would want just that). However, 
>> in your particular example, you want to represent a specific lion in 
>> the San Diego Zoo as a class, and that's a problem. A class of what? 
>> What are instances of this class? etc.
> I think I see what you mean. If we are looking at a lion, we know that 
> we can't be any more specific. Therefore classes should not be used 
> for things that can be pointed to. (But inversely, things that do not 
> exist may still be considered to be things...)
> Incidently, how do you best translate rdf:type and rdfs:subClassOf 
> into natural language without loosing the distinction between the two 
> terms? ("is a" seems to be used for both...)

The explanation that I often found useful is to think of classes as 
sets of their instances (so, the class of Lions is a set of all lions). 
Then subclass-of is a subset relationship  (the set of African lions is 
a subset of a set of all lions). instance-of is set membership: Simba 
is a member of the set of African lions (and lions, of course).

Received on Tuesday, 17 August 2004 17:10:16 UTC

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