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Model Theory

From: Ian Horrocks <horrocks@cs.man.ac.uk>
Date: Thu, 3 Jan 2002 18:55:41 +0000
Message-ID: <15412.43309.500168.687678@cs.man.ac.uk>
To: www-webont-wg@w3.org
To expand on the point I made at the end of the teleconf, I really
don't believe that this emphasis on model theory helps much w.r.t. the
point that Lynn was making, i.e., the question as to why I should
care.

As far as I am concerned, model theory is just one way (some would say
a very elegant way) of precisely specifying the meaning of the
language (its semantics). I think that the reason for needing such a
specification is pretty obvious: a language (particularly an ontology
language that is intended to be interpretable by "automated agents")
is of limited (zero?) utility if we can't be sure of the meaning of
what we write down in that language (yes, I know that natural language
works reasonably well for humans without satisfying this
requirement). Moreover, people writing/using software for the language
need a precise specification as to how it should behave and when it is
broken.

There is an argument that goes something like "the web will be full of
inconsistencies, so logical reasoning will be useless (everything will
be inconsistent), so why should we care about formal semantics". I
don't believe that this holds water for a variety of reasons including:

1) Usually we will only be dealing with a (very small) part of the
web. It is reasonable to ask if the information there is logically
consistent and useful to know if it isn't.

2) There is a big difference between an inconsistent ontology and web
pages that state contradictory facts w.r.t. an ontology - if I am
going to use/trust an ontology I would like to know that it is
logically consistent. As far as the web pages are concerned, if I know
that they are contradictory then I can make an informed decision about
how to deal with them.

Regards, Ian
Received on Thursday, 3 January 2002 13:56:02 GMT

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