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Re: Nothing in App. B of OWL Language Reference 31 March 2003

From: Guus Schreiber <schreiber@cs.vu.nl>
Date: Fri, 09 May 2003 14:39:12 +0200
Message-ID: <3EBBA170.3020304@cs.vu.nl>
To: "Richard H. McCullough" <rhm@cdepot.net>
CC: webont-comments at W3C <public-webont-comments@w3.org>

Dear Richard,

Thanks for your comment. Responses in-line.

Richard H. McCullough wrote:

> Appendix B says
> 
> <Class rdf:ID="Thing">
>   <rdfs:label>Thing</rdfs:label>
>   <unionOf rdf:parseType="Collection">
>     <Class rdf:about="#Nothing"/>
>     <Class>
>       <complementOf rdf:resource="#Nothing"/>
>     </Class>
>   </unionOf>
> </Class>
> 
> <Class rdf:ID="Nothing">
>   <rdfs:label>Nothing</rdfs:label>
>   <complementOf rdf:resource="#Thing"/>
> </Class>
> 
> Since the 2nd group implies that complementOf Nothing is Thing,
> the first group is equivalent to
> 
> <Class rdf:ID="Thing">
>   <rdfs:label>Thing</rdfs:label>
>   <unionOf rdf:parseType="Collection">
>     <Class rdf:about="#Nothing"/>
>     <Class rdf about="#Thing"/>
>   </unionOf>
> </Class>

The class axiom for owl:Thing in Appendix B of Reference defines its 
class extension to be the extension of owl:Nothing plus its complement, 
which means all individuals in the universe of discourse. owl:Nothing is 
its complement, so its class extension is the empty set.

Your revised axiom uses owl:Thing to define itself. We would prefer to 
refrain from such recursive definitions and thus keep to the axioms as 
they currently are.

> which is probably what you want to say,
> or else omit it all together.  
> 
> Even better would be to replace "Nothing" with
> some variant of "any Class" -- which I believe
> is what the document says elsewhere.

I'm not sure I understand your point. The extension of owl:Nothing is 
the empty set, so it is not "any Class".   owl:Thing and owl:Thing 
fulfill a special role, namely as root resp. leaf of the class lattice, 
cf. Sec. 3.1:

[[
Consequently, every OWL class is a subclass of owl:Thing and owl:Nothing 
is a subclass of every class.
]]

Please let us know whether this response is satisfactory.

Regards,
Guus Schreiber

> ============ 
> Dick McCullough 
> knowledge := man do identify od existent done;
> knowledge haspart proposition list;
> 
> 

-- 
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Received on Friday, 9 May 2003 08:39:15 GMT

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