Wooldridge, An Introduction to Multi Agent Systems

365 Pages·2005·4.87 MB·English

An Introduction to
MultiAgent
Systems
M I C H A EL W O O L D R I D GE
An introduction to
Multiaqent Systems
An Introduction to
Multiagent Systems
Michael Wooldridge
Department of Computer Science,
University of Liverpool, UK
JOHN WILEY & SONS, LTD
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Library of Congress Cataloging-in-Publication Data
Wooldridge, Michael J., I 9fi(>-
An introduction to multiagent systems / Michael Wooldridge.
p. cm.
Includes bibliographical references and index.
ISBN 0-471-4969 I-X
1. Intelligent agents (Computer software)—1. Title,
QA7G.76.158 VVG5 2001
00C.3 — dc21
2001055949
British Library Cataloguing in Publication Data
A catalogue record for this book is available from the British Library
ISBN 0 ,7\ 49691 X
Typeset in 9.5/12.5pt l.ucida Bright by T&r Productions Ltd, London.
Printed and bound in Great Britain by Biddies Ltd, Guildford and Kings Lynn.
This book is printed on acid-free paper responsibly manufactured from sustainable
forestry in which at least two trees are planted for each one used for paper production.
To my family:
Jean, John, Andrew,
Christopher, and of course Janine.
Contents
Preface xi
1 Introduction 1
1.1 The Vision Thing 4
1.2 Some Views of the Field 7
1.3 Objections to Multiagent Systems 8
2 Intelligent Agents 15
2.1 Environments 1 7
2.2 Intelligent Agents 23
?3 Agents and Objects 25
2.4 Agents and Expert Systems 27
2.5 Agents as Intentional Systems 28
2.6 Abstract Architectures for Intelligent Agents 31
2.7 How to Tell an Agent What to Do 36
2.8 Synthesizing Agents 42
J Deductive Reasoning Agents 47
3.1 Agents as Theorem Provers 49
3.2 Agent-Oriented Programming 54
3.3 Concurrent MetateM 56
4 Practical Reasoning Agents 65
4.1 Practical Reasoning Equals Deliberation Plus Means-Ends Reasoning 65
4.2 Means-Ends Reasoning 70
4.3 Implementing a Practical Reasoning Agent 75
4.4 HOMER: an Agent That Plans 80
4Jj The Procedural Reasoning Systpm 82
5 Reactive and Hybrid Agents 89
5.1 Brooks and the Subsumption Architecture 90
5.2 The Limitations of Reactive Agents 96
5.3 Hybrid Agents 97
5.3.1 TouringMachines 99
5T3T2 InteRRaP Wi
6 Multiagent Interactions 105
6.1 Utilities and Preferences 106
viii Contents
6.2 Multiagent Encounters 108
6.3 Dominant Strategies and Nash Equilibria 111
6.4 Competitive and Zero-Sum Interactions 113
6.5 The Prisoner's Dilemma 114
6.6 Other Symmetric 2x2 Interactions 122
6.7 Dependence Relations in Multiagent Systems 125
7 Reaching Agreements 129
7.1 Mechanism Design 130
7.? Auctions 131
7.3 Negotiation 137
7.3.1 Task-oriented domains 139
7.3.2 Worth-oriented domains 146
7.4 Argumentation 148
8 Communication 163
8.1 Speech Acts 164
8.1.1 Austin 164
8.1.2 Searle 165
8.1.3 The plan-based theory of speech acts 166
8.1.4 Speech acts as rational action 167
8.2 Agent Communication Languages 168
8.2.1 KIF 169
8.2.2 KQML 170
8.2.3 The FIPA agent communication languages T75
8.3 Ontologies for Agent Communication 180
8.4 Coordination Languages 183
9 Working Together 189
9.1 Cooperative Distributed Problem Solving 190
9.2 Task Sharing and Result Sharing 192
9.2.1 Task sharing in the Contract Net 194
9.3 Result Sharing 197
9.4 Combining Task and Result Sharing 197
9.5 Handling Inconsistency 199
9.6 Coordination 200
9.6.1 Coordination through partial global planning 202
9.6.2 Coordination through joint intentions 204
9.6.3 Coordination by mutual modelling 210
9.6.4 Coordination by norms and social laws 213
9.7 Multiagent Planning and Synchronization 218
10 Methodologies 225
10.1 When is an Agent-Based Solution Appropriate? 225
10.2 Agent-Oriented Analysis and Design Techniques 226
tt);3 Pitfalls of Agent Development 21J3
10.4 Mobile Agents 236
11 Applications 245
11.1 Agents for Workflow and Business Process Management 245
11.2 Agents for Distributed Sensing 248
11.3 Agents for Information Retrieval and Management 248
11.4 Agents for Electronic Commerce 254
Contents ix
11.5 Agents for Human-Computer Interfaces 258
11.6 Agents for Virtual Environments 259
11.7 Agents for Social Simulation 259
1L8 Agents for X 261
12 Logics for Multiagent Systems 267
12J Why Modal Logic? 268
12.2 Possible-Worlds Semantics for Modal Logics 270
12.3 Normal Modal Logics 271
12.4 Epistemic Logic for Multiagent Systems 278
12.5 Pro-attitudes: Goals and Desires 280
12.6 Common and Distributed knowledge 281
12.7 Integrated Theories of Agency 283
12.8 Formal Methods in Agent-Oriented Software Engineering 288
12.8.1 Formal methods in specification 288
12.8.2 Formal methods in implementation 290
12.8.3 Verification 294
Appendix A. A History Lesson 303
Afterword 317
References 319
Index 343
Preface
Multiagent systems are systems composed of multiple interacting computing ele-
ments, known as agents. Agents are computer systems with two important capa-
bilities. First, they are at least to some extent capable of autonomous action - of
deciding for themselves what they need to do in order to satisfy their design objec-
Lives. Second, they are capable of interacting with other agenls - not simply by
exchanging data, but by engaging in analogues of the kind of social activity that
we all engage in every day of our lives: cooperation, coordination, negotiation,
and the like.
—Multiagent systems are a relatively new sub-field of computer science - they
have only been studied since about 1980, and the field has only gained widespread
recognition since about the mid-1 QQOs. However, since then international interest
in the field has grown enormously. This rapid growth has been spurred at least in
part by the belief that agents are an appropriate software paradigm through which
to exploit the possibilities presented by massive open distributed systems - such
as the Internet. Although they will certainly have a pivotal role to play in exploiting
the potential of the Internet, there is a lot more to multiagent systems than this.
Multiagent systems seem to be a natural metaphor for understanding and building
a wide range of what we might crudely call artificial social systems. The ideas of
multiagent systems are not tied to a single application domain, but, like objects
before them, seem to find currency in a host of different application domains.
My intention in writing this book is simple. I aim to introduce the main issues in
the theory and practice of multiagent systems in a way that will be accessible to
anyone with a basic background in computer science/IT. The book is deliberately
intended to sit on the fence between science and engineering. Thus, as well as
discussing the principles and issues in the theory of multiagent systems (i.e. the
science of multiagent systems), I very much hope that I manage to communicate
something of how to build such systems (i.e. multiagent systems engineering).
The multiagent systems field can be understood as consisting of two closely
interwoven strands of work. The first is concerned with individual agents, while
the second is concerned with collections of these agents. The structure of the book
reflects this division. The first part of the book - Chapter 1 - sets the scene by
discussing where the multiagent system field emerged from, and presenting some
xii Preface
visions of where it is going. The second part - Chapters 2-5 inclusive—arc con-
cerned with individual agents. Following an introduction to the concept of agents,
their environments, and the various ways in which we might tell agents what to
do, I describe and contrast the main techniques that have been proposed in the
literature for building agents. Thus I discuss agents that decide what to do via
logical deduction, agents in which decision making resembles the process of prac-
tical reasoning in humans, agents that do not explicitly reason at all, and, finally,
agents that make decisions by combining deductive and other decision-making
mechanisms. In the third part of the book - Chapters 6-10 inclusive - 1 focus on
collections of agents. Following a discussion on the various ways in which multi-
agent encounters and interactions can be classified, I discuss the ways in which
self-interested agents can reach agreements, communicate with one another, and
work together. 1 also discuss some of the main approaches proposed for designing
multiagent systems. The fourth and final part of the book presents two advanced
supplemental chapters, on applications of agent systems, and formal methods
for reasoning about agent systems, respectively.
I have assumed that the main audience for the book will be undergraduate
students of computer science/IT - the book should be suitable for such students
in their second or third year of study. However, I also hope that the book will be
accessible to coniputing/TT professionals, who wish to know more about some of
the ideas driving one of the major areas of research and development activity in
computing today.
Prerequisites: what you need to know before you start
The book assumes a knowledge of computer science that would be gained in the
first year or two of a computing or information technology degree course. In order
of decreasing importance, the specific skills required in order to understand and
make the most of the book are
• an understanding of the principles of programming in high level languages
such as C or Java, the ability to make sense of pseudo-code descriptions of
algorithms, and a nodding acquaintance with some of the issues in concur-
rent and distributed systems (e.g. threads in Java);
• familiarity with the basic concepts and issues of artificial intelligence (such
as the role of search and knowledge representation);
• familiarity' with basic set and logic notation (e.g. an understanding of what
is meant by such symbols as e, c, n, u, A, V, ->, V, 3, h, \=).
However, in order to gain some value from the book, all that is really required is
an appreciation of what computing is about. There is not much by way of abstract
mathematics in the book, and wherever there is a quantity n of mathematics, I
have tried to compensate by including at least 2n intuition to accompany and
explain it.