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Re: [ontology-summit] PLEASE, PLEASE!!

To: <ontology-summit@xxxxxxxxxxxxxxxx>
From: "Obrst, Leo J." <lobrst@xxxxxxxxx>
Date: Mon, 5 Mar 2007 17:07:10 -0500
Message-id: <9F771CF826DE9A42B548A08D90EDEA8001A765BF@xxxxxxxxxxxxxxxxx>

I apologize, Nicola, if I introduced distraction. I meant to add to the expressiveness sidebar only.

Leo
--------------------------
Dr. Leo Obrst, MITRE, Information Semantics, lobrst@xxxxxxxxx, 703-983-6770

----- Original Message -----
From: ontology-summit-bounces@xxxxxxxxxxxxxxxx <ontology-summit-bounces@xxxxxxxxxxxxxxxx>
To: Ontology Summit 2007 Forum <ontology-summit@xxxxxxxxxxxxxxxx>
Sent: Mon Mar 05 16:48:36 2007
Subject: [ontology-summit] PLEASE, PLEASE!!

Folks,

these discussions are very nice, but I don't think they are directly related to the main focus of this list, i.e. the Ontology Summit 2007, which is supposed to concentrate on the question "what is an ontology".

I am already having a VERY hard time following the ontology summit discussion, and these recent messages don't really help to keep the discussion focused.

I am afraid I have just to give up any kind of active presence if the discussion on this list goes out of its main focus.

Best,

Nicola

On 5 Mar 2007, at 22:31, John F. Sowa wrote:


        Leo,

        To continue my point that efficiency *always* depends
        on what you're trying to do, I would like to address the
        problem of finding a consistent set of constraints:


                I, as usual, recommend the
                description logic complexity navigator:
                   http://www.cs.man.ac.uk/~ezolin/logic/complexity.html


        Given a set of arbitrary first-order constraints, the problem
        of proving consistency is NP complete.  Yet every SQL database
        permits arbitrary first-order constraints.

        Q: How is possible to prove that the constraints are consistent?

        A: Trivially.

        The point is that no database designer *ever* begins with
        an arbitrary set of constraints.  They *always* begin with
        some actual data -- a sample DB that shows what kind of data
        they expect to work with.

        That sample DB consists of a set of entities and a set of
        relations that are assumed to be true of those entities.
        In other words, the starting point is a Tarski-style model.

        Although *finding* a model is NP complete, the task of
        *checking* constraints is trivial, if a model is given.

        Given a proposed set of first-order constraints that do not
        depend on any recursive definitions -- i.e., anything expressible
        in SQL WHERE clauses -- the evaluation time in terms of a sample
        model takes, in the worst case -- polynomial time.

        If all the constraints turn out to be true of the model, then
        they are consistent.  If any of them turn out to be false,
        either throw them away or revise them to make them true.

        Bottom line:  If you're trying to define axioms or definitions
        for an ontology, a database, or a knowledge base, it's a good
        idea to start with at least one illustrative example.

        John


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Nicola Guarino

Editor in Chief, Applied Ontology (IOS Press)

Head, Laboratory for Applied Ontology (LOA), ISTC-CNR

Institute for Cognitive Sciences and Technologies

National Research Council




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