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From: ylkingsbury@watdragon.waterloo.edu (Yvonne Kingsbury)
Newsgroups: ont.events,uw.talks,uw.cs.grad
Subject: ICR Colloquium
Keywords: Hirofumi Katsuno will speak on "A Unified View of Propositional Know-  ledge Base Updates" on Wed., Aug. 2, 1989 at 3:30 in DC 1302.
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Date: 26 Jul 89 15:11:02 GMT
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                 The University of Waterloo
                   200 University Avenue
                     Waterloo, Ontario


         The Institute of Computer Research (ICR)

                  Presents a Colloquium on


   A Unified View of Propositional Knowledge Base Updates



by   Hirofumi Katsuno

of   NTT Basic Research Laboratories, Tokyo, Japan




ABSTRACT

The semantics of revising knowledge bases represented by sets of
propositional sentences is analyzed from a model-theoretic point of
view.  The operation which incorporates new knowledge into knowledge
base is called  revision.  A characterization of all revision
schemes that satisfy the Gardenfors rationality postulates is
given in terms of an ordering among interpretations.  A different kind
of change occurs when a sentence previously believed becomes
questionable; the operation that makes this change is called
contraction.  Properties of the contraction operator that can be
defined in terms of revision are also studied.  Two new update
operators, elimination and recovery, are introduced.
Elimination discards all previous preconceptions on a set of
propositional letters; recovery undoes the effect of the last update.
It is shown that elimination cannot be expressed as a contraction, and
that recovery is in general impossible.  The existence of an invariant
part of the knowledge base comprising a set of integrity constraints
is considered and the definition of revision and contraction are
modified to take integrity constraints into account.

This is joint work with Alberto O. Mendelzon.



Wednesday, August 2, 1989
3:30 p.m.
William G. Davis Computer Research Centre, Room 1302

Everyone is welcome.  Refreshments served.