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Re: [OWLWG-COMMENT] Defining the universal property in OWL-1.1

From: Carsten Lutz <clu@tcs.inf.tu-dresden.de>
Date: Sun, 11 Nov 2007 20:38:59 +0100 (CET)
To: Michael Schneider <schneid@fzi.de>
Cc: Owl Dev <public-owl-dev@w3.org>, gstoil@image.ece.ntua.gr, boris.motik@comlab.ox.ac.uk
Message-id: <Pine.LNX.4.64.0711112029110.24999@frege.inf.tu-dresden.de>

Hi Michael,

> This week in the OWL-WG mailing list, there was some discussion about
> introducing the "universial property" into OWL-1.1.

I agree with what you say. Your encoding trick is a variation of what
is often called a "spypoint" (an element that sees all other elements),
see e.g. the paper "A Road-map on Complexity for Hybrid Logic" by 
Areces, Blackburn, and Marx.

Just one remark, namely that one should be a bit careful here. First,
different ontologies using your encoding may use different names
for the universal role. Second, even if they use the same name, they
may use different names for the individual (spypoint) in the encoding.
For this reason, you are actually not *defining* the universal role in
a strict logical sense. I would maybe call it a projective definition.

However, the point is that there are subtle differences. In particular, 
if you are interested in the reasoning task of ontology entailment ("does
one ontology entail another?") you run into trouble if the two ontologies
use different role/individual name (whereas this is no problem for
satisfiability, subsumption, classification, etc). Regarding the discussion
on OWL-WG, this means that your construction cannot be used to define true
anonymous individuals.

An obvious remedy is to have a convention for the name of the role
which is defined to be universal. But then, that's the same as
explicitly introducing a universal role into OWL, i.e., just what I
have proposed.


*      Carsten Lutz, Institut f"ur Theoretische Informatik, TU Dresden       *
*     Office phone:++49 351 46339171   mailto:lutz@tcs.inf.tu-dresden.de     *
Received on Sunday, 11 November 2007 19:39:20 UTC

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