DS-2000-01: Resource Bounded Belief Revision

DS-2000-01: Wassermann, Renata (2000) Resource Bounded Belief Revision. Doctoral thesis, University of Amsterdam.

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Abstract

%Nr: DS-2000-01
%Author: Renata Wasserman
%Title: Resource Bounded Belief Revision

The problem of belief revision has been extensively studied during the
last twenty years. Given an agent with a set of (ascribed) beliefs,
how should he change his beliefs when confronted with new information?
This is the most general formulation of the problem of belief
revision. An agent may be a human being, a computer program or any
kind of system to which one can ascribe beliefs and from which one
would expect rational reactions.

This is a multidisciplinary problem, with applications to several
areas. We can give some examples of belief revision as it appears in:

* Daily life: I believed it was always raining in Amsterdam. One
morning I woke up in Amsterdam and the sun was shining. I believed
that on that day the weather was fine, contradicting my previous
belief. I had to give up my belief that it always rained there.

* Databases: In the database containing data about the customers of a
bookstore, there is an entry for John Smith, with his date of birth
being 20/2/67. I get then a new order, where John Smith's date of
birth is 20/2/76. I cannot add another date of birth and John's
date of birth cannot have changed with time. I have to decide what
to do. Keep the old data? Substitute it by the new? Or is it
another John Smith after all, who should be added to the database?

* Robotics: A mobile robot has a map of the environment where it is
supposed to move. On the map, there is nothing in front of it, so
it should be able to move straight. But then its sensors indicate
the presence of a big object in front of the robot. Should it doubt
its sensors and continue trying to move straight? Or should it
believe its sensors and doubt the map?

* Diagnosis: I believe that if I put an article at the right position
on a properly working copying machine, I get copies of the
article. Suppose I put an article at the right position, but all I
get are blank pages. Should I give up my belief that I chose the
right position? Or should I give up the belief that the copying
machine is working properly?

Belief revision has been extensively studied in philosophy for
extremely idealized agents. The agents considered are infinite beings,
without any limitation of memory, time, or deductive ability. However,
adapting these solutions to less idealized agents is far from
trivial. In order to solve the problems cited above in a way which can
be used by real agents, one has to consider that any realizable agent
is a finite being and that calculations take time [Che86]. We need a
theory which takes these characteristics -- finiteness, memory and
time limitations -- into account.

Departing from the standard logical model for belief revision, the
main goal of the present work is to find a theory that can be applied
to more realistic agents. We stress here that our purpose is not to
find a computational implementation of existing theories, but to
elaborate a theory for less idealized agents.

In a recent paper, Chopra and Parikh [CP99] presented some desiderata
for a belief revision formalism which we also see as our goals:
distinction between explicit and implicit beliefs, no trivialization
in the presence of inconsistencies, computational tractability, and
minimal change.

The main achievements of our work are:

1. Formalization of a richer notion of belief state, based on the
informal works of Harman and Cherniak (Chapter 4).

2. Generalization of standard results found in the literature,
allowing for the use of more general logics (Chapter 5). This part
is joint work with Sven Ove Hansson.

3. Design of a psychologically motivated, computationally efficient
method for focussing on the relevant part of a belief state
(Chapter 6).

4. Application of the developed framework to the problem of
model-based diagnosis and use of the computational tools from
model-based diagnosis for implementing belief revision operators
(Chapter 7).

Item Type:	Thesis (Doctoral)
Report Nr:	DS-2000-01
Series Name:	ILLC Dissertation (DS) Series
Year:	2000
Subjects:	Computation Logic Philosophy
Depositing User:	Dr Marco Vervoort
Date Deposited:	14 Jun 2022 15:16
Last Modified:	14 Jun 2022 15:16
URI:	https://eprints.illc.uva.nl/id/eprint/2013

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