Craig Boutilier
Department of Computer Science
University of British Columbia
Vancouver, BC, CANADA, V6T 1Z4
email: cebly@cs.ubc.ca
Abstract
Belief revision and belief update have been proposed as two
types of belief change serving different purposes. Belief
revision, as exemplified by the classic AGM theory, is intended
to capture changes of an agent's belief state reflecting new information
about a static world. Belief update, as specified by Katsuno and
Mendelzon, is intended to capture changes of belief in response to
a changing world. We argue that both belief revision and
belief update are too restrictive; routine belief change involves
elements of both. We present a model for generalized update
that allows updates in response to external changes to inform the
agent about its prior beliefs. This model of update combines aspects
of revision and update, providing a
more realistic characterization of belief change. We show that, under
certain assumptions, the original update postulates are satisfied.
We also demonstrate the plain revision and plain update are special
cases of our model, in a way that formally verifies the
intuition that revision is suitable for ``static'' belief change.
Appeared IJCAI-95
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