Understanding Agent Systems

248 Pages·2004·4.48 MB·English

by  Mark d’Inverno

Springer Series on Agent Technology
Series Editor: T. Ishida N. Jennings K. Sycara
Springer-Verlag Berlin Heidelberg GmbH
Mark d'Inverno Michael Luck
Understanding
Agent Systems
Second Edition, Revised and Extended
With 42 Figures
, Springer
Mark d'Inverno Michael Luck
Cavendish School School ofElectronic s
of Computer Science and Computer Science
Univeristy of Westminster University of Southampton
9-18 Euston Centre Southampton SOl? lBJ
LondonNW13ET United Kingdom
Uni ted Kindom mm/@ecs.soton.ac.uk
[email protected]
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ISBN 978-3-642-07382-3 ISBN 978-3-662-10702-7 (eBook)
DOI 10.1007/978-3-662-10702-7
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© Springer-Verlag Berlin Heidelberg 200 I, 2004
Originally published by Springer-Verlag Berlin Heidelberg N ew Y ork in 2004
Softcover reprint of the hardcover 2nd edition 2004
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Preface to the Second Edition
Since the first edition was published two years ago, much has been done on extend
ing the work done on SMART to address new and important areas [3-5,54,79,80,
108-110,116,118-120,122]. In this second edition, we have revised, updated and
corrected the existing text and added three new chapters. These chapters provide a
broader coverage of the fie1d of agents, and show in more detail how the specific
framework described can be used to examine other areas. In Chapter 6, we use the
concepts of discovery to apply the framework to autonomous interaction in multi
agent systems; in Chapter 10 we use it for considering normative agents and sys
tems; and in Chapter 11 we describe work on an implementation and development
environment.
As a course text, the book can be considered in different parts, as follows.
- Chapter I and Chapter 2 offer a basic introduction to agents and their core com
ponents.
- Chapter 3 and Chapter 4 cover relationships between agents and basic notions of
cooperation for multi-agent systems.
- Chapter 5 and Chapter 6 introduce sociological agents, which are needed for rea
soning and planning, and their use in reasoning about communication and inter
action.
- Chapter 7, Chapter 8, Chapter 9 and Chapter 10 each cover different application
areas relating to different aspects, inc1uding coordination (through the contract
net), agent architecture (through AgentSpeak(L), social dependence networks,
and normative systems.
- Chapter 11 offers a different perspective in showing how practical systems may
be constructed based on the key notions of the book.
There is now a book website at:
www.ecs.soton.ac.ukj-mmljuasj
Overview of the book
Chapter 1 reviews the agent landscape, outlining the key concepts of agent-based
systems and some of the difficu1ties that have arisen, particu1arly in relation to def
inition and characterisation of agents. It makes reference to numerous reviews and
VI Preface to the Second Edition
definitions and shows just how varied the attitudes towards agents are. The chapter
ends with an introduction to the methodology used in the book: the need for a formal
framework, the choice of the Z specification language, and the style of presentation
that is used throughout.
Chapter 2 is perhaps the most fundamental chapter in the book, providing fuB
details of the SMART agent framework that underpins everything else. It begins with
the introduction of the primitive notions used, and moves on to define the different
kinds of entity that exist in OUf fOUf-tiered agent hierarchy, considering both action
and perception along the way. Here agents are distinguished from both objects and
autonomous agents in a clear and detailed fashion, both intuitively and mathemati
cally.
The relationships between agents are the subject of Chapter 3, arising as anatural
consequence of the basic definitions of agents from the previous chapter. In partic
ular, goal adoption is seen as the critical mechanism underlying multi-agent sys
tems, with the notions of engagement of one agent by another and the cooperation
of two autonomous agents resulting directly from it. These relationships are anal
ysed further to arrive at a more sophisticated taxonomy of inter-agent relationships.
Chapter 4 complements this by describing the ways in which these relationships
can be created and destroyed. One of our key motivations is to remain connected to
issues of implementation, requiring just such an operational account as weB as the
declarative one of Chapter 3.
In Chapter 5, the SMART framework is further developed to include different di
mensions of agents that are necessary for their effective operation in multi-agent
systems in dynarnic and open environments. In particular, the chapter considers
various aspects of agent modelling as weB as the incorporation of plans for more
complex action and interaction. One key result here is the construction of a taxon
omy of plan and agent categories that are useful for agents to better understand their
environments and to take greater advantage of them. Chapter 6 then describes the
combination of SMART and concepts from discovery to give a model for autonomous
interaction in which agents use their models of other to reason about communication
and interaction.
The remaining chapters are concemed with the development of case studies to
illustrate the application of the SMART framework to a range of diverse systems and
theories. Chapter 7 shows how the contract net protocol is easily captured within the
framework; Chapter 8 demonstrates its applicability to a BDI architecture, AgentS
peak(L); Chapter 9 shows how it can be used to reformulate, and identify limiting
assumptions in, a rather different theoretical model, Social Power Theory, and its
computational counterpart, Social Dependence Networks; and Chapter 10 offers a
model for normative agents, showing how different kinds of norms can be repre
sen ted and how agents can operate in normative societies.
Finally, Chapter 11 describes some initial work on implementing SMART using
the actSMART environment, before Chapter 12 reviews the overall contribution of
the book, and evaluates the applicability and generality of SMART. In all this, each
chapter provides an intuitive conceptual description of the basic concepts, and aug-
Preface to the Second Edition VII
ments it with a formal specification in Z. Both of these aspects are intended to be
self contained, with adequate explanation to make sense of the formalisation in most
cases, even for those without prior knowledge of the Z language.
Acknowledgements
This book is now in its second edition. From the development of the initial idea of
publishing this work as a book, Alfred Hofmann at Springer has provided support
and encouragement. He has now seen the book through to completion twice, and we
very much value and appreciate his efforts. Thanks also to Ingeborg Mayer, Uwe
Matrisch and Gabi Fischer who worked with us to ensure that the final manuscript
and camera-ready copy were just right.
In addition to those who were acknowledged for the first edition, we must also
mention others in this new edition. Thanks to colleagues who helped with discus
sion, debate and sometimes disagreement: Peter McBumey, Pietro Panzarasa and
Chris Preist. Again, our students and research fellows contributed to specific correc
tions and to the general presentation: Arturo Avila Rosas, Jorge GonzaIez Palacios,
Eletheria Kyriazidou and Steve Munroe. In particular, we would like to thank Ioan
nis Svigkos and Lourival Paulino da Silva who both isolated a number of errors in
the first edition.
Thanks also to Abha, Jo and Leo, Jeremy and Monica (and Francesca and Mar
tina), Dan and Franky (and Poppy), Lucy, Catherine, John and Philippa, Guido and
Betty (and Giacomo and Alice), Rachel, Orly, Rona, Erzsebet, Judith and Shaun,
Julia and Derek, Claudia, Doug and Alexis (and Rosie), Nick and Rachel, Chris,
Rajesh, Hyo Young, Dawn and Stephen, Sharon and Ben (and Daniel, Jonathan and
Francesca) Marcia, Val, Debbie, Christine, Eileen, Susan, Nicky, Serena, Liz, Carla,
Dolly and Candy (and Tiger and Hector), Eli, Phil and Geddy (and Michael and
Daisy), Paul Rooney, Gi and Philly (and Beany, Tatti, Oscar, Flo and Rose), Andy
and Mel (and Thomas and Max), Neil and Susi (and Alex and Olly), Tim and Lisa
(and Joseph), Dave and Jo (and Saskia), Karen and Jason (and Tali), Val and Bill,
Vijay and Lisa, Chris and Catherine (and Eliza), Emma Barrett, Ali and Dave, Chris
and Secha, Nicki and Tony, Nicki and Giles, Chris and Sylvia, Tony and Leslie,
Polly and Antonia, Eli, Lisa Rigg, Mike Freeman, Mike Bacon, Jenny Goodwin,
Kellie Samuda, Mo City, Hutch, Gib, Lawso, Dicks and the Lab Bar in Soho, the
Guinea Grill, the weekenders cricket club, and Choral Clench, all of whom have
distracted us so easily.
London and Southampton Michael Luck
June 2003 Mark d'Inverno
Preface to the First Edition
Around ten years ago, when we were both PhD students, working on different but
related aspects of artificial intelligence, we shared an office in the furthest corner of
the Department of Computer Science at Vniversity College London. Our friendship
began then, but our professional collaboration only really got going when we both
left, one of us moving the few yards to the Vniversity of Westminster and the other
further afield to the Vniversity of Warwick and later the Vniversity of Southampton.
Nevertheless, we can trace back many of OUf inspirations to those days at VCL, in
discussions with Derek Long, John Campbell, Maria Fox and John Wolstencroft,
who all contributed to our initial enthusiasm for working in this area.
On leaving VCL, however, we tried to bring OUf research interests together in the
newly emerging area of agent-based systems, but found difficulties in communica
tion with each other over basic terms and concepts, simply due to the immaturity of
the field. In other words, the problems we had in finding a base on which to develop
OUf ideas set us on a long path, over a number of years, resulting in our construction
and refinement of a conceptual framework within which to define, analyse and ex
plore different aspects of agents and multi-agents systems. This is the work reported
in this book.
The work described here is the result of a number of years of joint work, and
is reported in several journal and conference papers published in that time [43-
51,56,86,112-115,117,121]. We would like to take this opportunity to thank the
anonymous referees who have provided useful comments and feedback for those
articles, and also to make special mention of Alfred Hofmann at Springer who has
seen this book through to completion.
Perhaps more important has been the support we have had from colleagues, fam
ily and friends, at work and home, who provided an environment that encouraged us
in OUf research. Particular thanks should go to Paul Howells, Nick Jennings, Mike
Joy, Sara Kalvala, Muthu Muthukrishnan, Mark Priestly, Maarten de Rijke and Steve
Winter, who provided support from within our own institutions.
Colleagues at other institutions have also helped greatly with discussion, debate
and sometimes disagreement over OUf work in particular, and agent-based systems
in general. Thanks to Cristiano Castelfranchi, Alex Coddington, Rosaria Conte, Jon
Crowcroft, Rogier van Eijk, Michael Fisher, Stan Franklin, Mike Georgeff, Suran
Goonatilake, Koen Hindriks, Wiebe van der Hoek, David Kinny, John-Jules Meyer,
Jörg Müller, Simon Parsons, Anand Rao, Mike Wooldridge, and Chengqi Zhang.
X Preface to the First Edition
Many of OUf students and research fellows also helped along the way by identify
ing errors, problems, and generally causing OUf presentation to be enhanced: Ronald
Ashri, Kevin Bryson, Sorabain de Lioncourt, Nathan Griffiths, Fabiola Lopez y
Lopez, Simon Miles, Alex Poylisher and Craig Tunstall.
Thanks also to Abha, Jo and Leo, Jeremy and Monica (and Francesca and Mar
tina), Dan and Franky, Lucy, Catherine, John and Philippa, Guido and Betty, Rachel,
Orly, Rona, Erzsebet, Sharon and Ben (and Daniel, Jonathan and Francesca) Mar
cia, Val, Debbie, Christine, Carla, Dolly and Candy (and Tiger and Hector), Phil and
Geddy (and Michael and Daisy), Gi and Philly (and Beany, Tatti, Oscar and Flo),
Andy and Mel (and Thomas and.Max), Neil and Susi (and Alex and Olly), Tim
and Lisa, Dave and Jo, Karen and Jason, Val and Bill, Emma, Ali and Dave, Chris
and Secha, Jenny, Nicki and Tony, Nicki and Giles, Chris and Sylvia, Tony and
Leslie, Polly and Antonia, Lisa Rigg, Mike Freeman, Mike Bacon, Dicks, Hutch,
Gib, Lawso, Banksy, Pog, the Lab Bar, Weekenders C.C. and Choral Clench, all of
whom have distracted us so easily.
Finally, special thanks to both sets of parents.
London and Southampton Michael Luck
February 200 I Mark d'Inverno
Contents
1. The Agent Landscape ....................................... .
1.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Agents.................................................... 3
1.2.1 Terminology.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2.2 Problems with Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.3 Multi-Agent Systems ....................................... 6
1.4 Desiderata for a Conceptual View of Agents . . . . . . . . . . . . . . . . . . . . 7
1.5 A Formal Framework for Agent Definition and Development . . . . . . 8
1.5.1 Formal Frameworks .. ..... ..... .. . ....... .. . .. ..... .. 8
1.5.2 Notation............................................ 9
1.5.3 Specification Structure Diagrams . . . . . . . . . . . . . . . . . . . . . .. 10
2. The SMART Agent Framework ................................ 15
2.1 Introduction........... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 15
2.2 Initial Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 15
2.3 Entities................................................... 19
2.3.1 Entity State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 20
2.3.2 Entity Operations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 21
2.4 Objects................................................... 21
2.4.1 Object Behaviour . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 22
2.4.2 Object State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 22
2.4.3 Object Operations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 23
2.5 Agents.................................................... 24
2.5.1 Introduction ......................................... 24
2.5.2 Agent Specification .................................. 24
2.5.3 Agent Perception .... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 26
2.5.4 Agent Action. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 27
2.5.5 Agent State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 27
2.5.6 Agent Operations .................................... 28
2.6 Autonomy................................................ 29
2.6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 29
2.6.2 Autonomous Agent Specification . . . . . . . . . . . . . . . . . . . . . .. 30
2.6.3 Autonomous Agent Perception . . . . . . . . . . . . . . . . . . . . . . . .. 31
2.6.4 Autonomous Agent Action . . . . . . . . . . . . . . . . . . . . . . . . . . .. 31