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From: SHARON@SU-SCORE.ARPA
Newsgroups: net.ai
Subject: Ph.D. Oral
Message-ID: <13651@sri-arpa.UUCP>
Date: Fri, 11-Nov-83 12:56:17 EST
Article-I.D.: sri-arpa.13651
Posted: Fri Nov 11 12:56:17 1983
Date-Received: Thu, 17-Nov-83 02:38:58 EST
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From:  Sharon Bergman <SHARON@SU-SCORE.ARPA>

                [Reprinted from the SU-SCORE bboard.]

                                  Ph.D. Oral

                       Tuesday, Nov. 15, 1983, 2:30 p.m.

                  Bldg. 170 (history corner), conference room

                          A DEDUCTIVE MODEL OF BELIEF

                                 Kurt Konolige


Reasoning about knowledge and belief of computer and human agents is assuming
increasing importance in Artificial Intelligence systems in the areas of
natural language understanding, planning, and knowledge  representation in
general.  Current formal models of belief that form the basis for most of these
systems are derivatives of possible- world semantics for belief.  However,,
this model suffers from epistemological and heuristic inadequacies.
Epistemologically, it assumes that agents know all the consequences of their
belief.  This assumption is clearly inaccurate, because it doesn't take into
account resource limitations on an agent's reasoning ability.  For example, if
an agent knows the rules of chess, it then follows in the possible- world model
that he knows whether white has a winning strategy or not.  On the heuristic
side, proposed mechanical deduction procedures have been first-order
axiomatizations of the possible-world belief.

A more natural model of belief is a deductions model:  an agent has a set of
initial beliefs about the world in some internal language, and a deduction
process for deriving some (but not necessarily all)  logical consequences of
these beliefs.  Within this model, it is possible to account for resource
limitations of an agent's deduction process; for example, one can model a
situation in which an agent knows the rules of chess but does not have the
computational  resources to search the complete game tree before making a move.

This thesis is an investigation of Gentzen-type formalization of the deductive
model of belief.  Several important original results are  proven.  Among these
are soundness and completeness theorems for a deductive belief logic; a
corespondence result that shows the possible- worlds model is a special case of
the deduction model; and a model analog ot Herbrand's Theorem for the belief
logic. Several other topics of knowledge and belief are explored in the thesis
from the viewpoint of the deduction model, including a theory of introspection
about self-beliefs, and a theory of circumscriptive ignorance, in which facts
an agent doesn't know are formalized by limiting or circumscribing the
information available to him.  Here it is!