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Fwd: Question re: HasKey entailments

From: Ian Horrocks <ian.horrocks@comlab.ox.ac.uk>
Date: Wed, 7 Jan 2009 22:47:23 +0000
Message-Id: <D39C0D1E-66F6-48B5-AFCC-A5752BB2EFDB@comlab.ox.ac.uk>
Cc: Jim Hendler <hendler@cs.rpi.edu>
To: public-owl-comments@w3.org

In the subsequent discussion (see [1] and thread) it was agreed that  
the relevant language features are satisfactory, but it was also  
stated that the feature needs to be better documented. I have  
forwarded this to the public comments list so that appropriate action  
can be taken.

Ian

[1] http://lists.w3.org/Archives/Public/public-owl-wg/2008Dec/0054.html

Begin forwarded message:

> Resent-From: public-owl-wg@w3.org
> From: Jim Hendler <hendler@cs.rpi.edu>
> Date: 29 December 2008 20:57:48 GMT
> To: OWL Working Group WG <public-owl-wg@w3.org>
> Subject: Question re: HasKey entailments
>
>
> (Since I'm not a member of the WG this can be considered a LC  
> comment or since my group is in the group, you can consider it an  
> internally discussible comment)
>
> I was talking to someone about keys and we were looking at the  
> document section on this (http://www.w3.org/2007/OWL/wiki/ 
> Syntax#Keys) where the example is given of
>
> HasKey( a:Person a:hasSSN ) 	
> PropertyAssertion( a:hasSSN a:Peter "123-45-6789" ) 	
> ClassAssertion( a:Person a:Peter ) 	
> PropertyAssertion( a:hasSSN a:Peter_Griffin "123-45-6789" ) 	
> ClassAssertion( a:Person a:Peter_Griffin ) 	
>
> and my colleague asked why the last axiom wasn't entailed by the  
> HasKey.  We went and looked in the model theory, and it says under  
> the circumstances of the first four expressions HasKey won't apply  
> (because there's no evidence of a CE for Peter_Griffin) -- so it  
> appears this is not entailed in the current model theory.
>  Guess my question is why does one need the additional condition  
> (and thus the additional axiom) -- wouldn't it follow that if  
> HasKey relates person's via hasSSN (i.e. the HasKey assertion) that  
> anything that has that key (the SSN) would have to be a person?
>  If HasKey would entail that the domain of the property asserted  
> would be the first argument to the HasKey (which is what seems to  
> be intended) then wouldn't the fact that X is an element of
> (CE)^^C [1] and in fact that it is a Person follow?
>    Is there a reason we don't do this ?-- would seem to simplify  
> the use of HasKey without causing an obvious semantic harm that I  
> can see (and would make its use more intuitive in many cases).
>    thanks
>    JH
>
>
>
>
> [1] sorry, my mailer doesn't seem to like the fonts from the  
> document - see http://www.w3.org/2007/OWL/wiki/Syntax#Keys fpr the
Received on Wednesday, 7 January 2009 22:48:03 GMT

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