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Re: Layering bug

From: pat hayes <phayes@ihmc.us>
Date: Wed, 2 Jul 2003 15:19:44 -0500
Message-Id: <p0600121abb28ecd603de@[]>
To: www-webont-wg@w3.org

Coming rather late to this discussion, I am surprised that OWL DL 
allows one to assert that the universe is empty. This would not 
normally be considered to be a consistent assertion in first-order 
logic (it would in a free logic, but free logics have other 
unintuitive properties). Allowing the universe to be empty means that 
assertions like

(forall (?x) (P(?x) and not P(?x)))

are consistent, since they are true in an interpretation with an 
empty universe. In fact, any universal assertion is true in such an 
interpretation, even (forall (?x) False). Is this really what one 
wants to have in OWL DL? It plays havoc with most proof systems for 
conventional logics, and would mean that OWL DL could not be 
translated into a conventional logical notation in a conventional way.

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Received on Wednesday, 2 July 2003 16:19:48 UTC

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