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Re: [ontolog-forum] Truth

To: "[ontolog-forum]" <ontolog-forum@xxxxxxxxxxxxxxxx>
From: Chris Menzel <chris.menzel@xxxxxxxxx>
Date: Fri, 6 Jul 2012 16:25:13 -0500
Message-id: <CAO_JD6Pn=DQkHAUpXFZ9E_emk2V2a88rPY9iPzpp3VrWvZ65GA@xxxxxxxxxxxxxx>
On Fri, Jul 6, 2012 at 4:05 PM, Michael Brunnbauer <brunni@xxxxxxxxxxxx> wrote:

Hello Matthew,

On Fri, Jul 06, 2012 at 09:35:02PM +0100, Matthew West wrote:
> CM> ... classes are extensional in OWL.
> Is that extensional in that the extension is the members declared in the OWL ontology, or is that extensional in the sense that the members define the class, but I might not know about all of them?

I think it's extensional in the sense that classes are not first class entities
but defined via the extension of the rdf:type property.


Actually, yes, there is an RDF-compatible semantics for OWL I'd forgotten about where OWL classes are simply entities that are assigned sets of individuals as their extensions. In this semantics, distinct classes can have the same "members". But IIRC in both the W3C "direct" semantics for OWL and the "model theoretic" semantics, OWL classes are simply sets of individuals.

Pat will probably jump in here and straighten me out...


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