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Re: LC reply drafted

From: Sebastian Rudolph <rudolph@aifb.uni-karlsruhe.de>
Date: Tue, 12 May 2009 23:24:34 +0200
To: Bijan Parsia <bparsia@cs.manchester.ac.uk>
Message-Id: <BEC29B15-FA93-4F47-95C0-697A2E82E16E@aifb.uni-karlsruhe.de>
Cc: W3C OWL Working Group <public-owl-wg@w3.org>

Am 12.05.2009 um 21:54 schrieb Bijan Parsia:

> On 12 May 2009, at 20:41, Sebastian Rudolph wrote:
>> Dear all,
>> if I interpreted the intention of the below LC comment correctly,  
>> Richard would like to see an explicit statement that classes just  
>> represent sets of individuals
> But that would be to say something false. OWL Classes most obviously  
> do not "just" represent sets of individuals (as they can be mapped  
> to distinct sets in different interpretations). If anything, OWL  
> Classes are first order logic formulae with one free variable (and  
> thus, when atomic, correspond to monadic predicates).

I don't see a problem with the current wording. Given a "state of  
affairs" (as we informally try to describe the notion of  
"interpretation" in Section 3), a class represents a set of  
individuals. Given another "state of affairs", the set might be  
different. I'm all in favour of being logically precise but letting  
"monadic predicates of first-order logic" enter the Primer-scene would  
IMHO not be particularly appropriate for the character of the document.

>> and that the notion of a "concept" is something related but  
>> different.
>> I tried to address this by adding two sentences to the Primer  
>> document, see the diff at
>> http://www.w3.org/2007/OWL/wiki/index.php?title=Primer&diff=23464&oldid=23440
> ""In modeling, classes are often used to denote the extension sets  
> of concepts of human thinking, like ''person'' or ''woman''."""
> But this is precisely wrong:
> 	http://en.wikipedia.org/wiki/Definition#Intension_and_extension
> (reductio ad wikipedia :)). So please don't use the word "extension".

Forgive me, but I don't find the contradiction that you may have  
spotted (besides being a bit sceptic about using wikipedia for an  
authoritative argument). In my understanding - which I believe is the  
common one - the extension (set) of a concept is the set of objects  
belonging to that concept, the extension of the concept "human" is the  
set of all humans etc. So what's wrong with that?


> The commentator has a strange idea of what a concept is (and of  
> class, and of set). I don't really want to import them into an  
> already tangled terminological situation.
>> Find the proposed draft response at:
>> http://www.w3.org/2007/OWL/wiki/LC2_Responses/RHM1
> In general, readers of the primer aren't going to know what  
> "extension set" (er... generally known as the *extension*) is, so  
> this wouldn't be clarificatory even if it were right.
> Cheers,
> Bijan.

Dr. Sebastian Rudolph
Institute AIFB, University of Karlsruhe, D-76128 Karlsruhe
rudolph@aifb.uni-karlsruhe.de    phone +49 (0)721 608 7362
www.sebastian-rudolph.de                 fax +49 (0)721 608 5998
Received on Tuesday, 12 May 2009 21:25:48 UTC

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