Agents that Reason and Negotiateby ArguingSIMON PARSONS, CARLES SIERRA and NICK JENNINGS,Department of Electronic Engineering, Queen Mary and WestfieldCollege, University of London, London El 4NS, U.K.E-mail: {S.D.Parsons,C.A.Sierra,N.R.Jennings}@qmw.ac.ukAbstractThe need for negotiation in multi-agent systems stems from the requirement for agents to solvethe problems posed by their interdependence upon one another. Negotiation provides a solutionto these problems by giving the agents the means to resolve their conflicting objectives, correctinconsistencies in their knowledge of other agents' world views, and coordinate a joint approachto domain tasks which benefits all the agents concerned. We propose a framework, based upon asystem of argumentation, which permits agents to negotiate in order to establish acceptable waysof solving problems. The framework provides a formal model of argumentation-based reasoning andnegotiation, details a design philosophy which ensures a clear link between the formal model andits practical instantiation, and describes a case study of this relationship for a particular class ofarchitectures (namely those for belief-desire-intention agents).Keywords: Argumentation, negotiation, multi-context systems, multi-agent systems, BDI agents.1 IntroductionAn increasing number of software applications are being conceived, designed, andimplemented using the notion of autonomous agents. These applications vary fromemail filtering [26], through electronic commerce [35, 47], to large industrial appli-cations [20]. In all of these disparate cases, however,the notion of autonomy is usedto denote the fact that the software has the ability to decide for itself which goalsit should adopt and how these goals should be achieved [48]. In most agent appli-cations, the autonomous components need to interact with one another because ofthe inherent interdependencies which exist between them. The predominant mech-anism for managing these interdependencies at run-time is negotiation—the processby which a group of agents communicate with one another to try and come to a mu-tually acceptable agreement on some matter [3]. Negotiation is so central preciselybecause the agents are autonomous. For an agent to influence an acquaintance, theacquaintance has to be persuaded that it should act in a particular way. The meansof achieving this state are to make proposals, trade options, offer concessions, and(hopefully) come to a mutually acceptable agreement—in other words to negotiate.We are interested in building autonomous agents which negotiate. This paper makesfour main contributions towards this goal. The first is to outline a generic model ofnegotiation for autonomous agents which need to persuade one another to act in aparticular way. The second is to describe an approach to building agent architectureswhich have a clear link between their specification and their implementation. OurJ. Logic Compntai., Vol. 8 No. 3, pp. 261-292 1998 © Oxford University Press262 Agents that Reason and Negotiate by Arguingapproach is founded upon the natural correspondence between multi-context systems[13], which allow distinct theoretical components to be defined and interrelated, andthe modularity present in agent architectures. To demonstrate the power and flexibil-ity of this approach a number of variants of the widely used Belief-Desire-Intention(BDI) agent model [32] are specified with the same conceptual structures. The thirdcontribution is to provide a general system of argumentation suitable for use by multi-context agents in a multi-agent environment, and to describe a specific version of thissystem which may be used by multi-context BDI agents. This is necessary becausethe move to both multi-context agents and then to BDI agents introduces additionalissues over and above those which are handled by existing systems of argumentation.The fourth contribution is to present a well-grounded framework for describing thereasoning process of negotiating agents. This framework is based upon the use ofargumentation both at the level of an agent's internal reasoning and at the level ofnegotiation between agents. Such an approach has been advocated (in a discursiverather than formal manner) by Hewitt [15] as the most natural means of viewing thereasoning and operation of truly autonomous agents in open systems.This paper builds on our previous work in the fields of negotiation and argumen-tation. It is an extension of the work presented in [28, 38] in that, respectively, itprovides a tighter integration of argumentation and the mental model of the negoti-ating agents, and it deals with arguments which justify positions (in addition to basicstatements about positions). It also fixes some technical problems with the model ofargumentation presented in [28]. The work described here is also complementary tothe work described in [39] in that it concentrates on the way in which arguments arebuilt and analysed rather than on the communication language and the negotiationprotocol.The remainder of the paper is structured so that each major contribution is pre-sented in a separate section. Section 2 introduces a general framework for describingnegotiation. Section 3 shows how multi-context systems can be used to specify agentarchitectures in general and BDI architectures in particular. Section 4 presents a sys-tem of argumentation suitable for use by multi-context agents in multi-agent systems.Section 5 illustrates how this framework can be used for argumentation-based nego-tiation. Section 6 then places our work in the context of previous work in the fieldsof multi-agent systems, negotiation and multi-context systems. Section 7 concludesand outlines a number of issues which require further investigation.2 A framework for negotiationExamination of the literature on negotiation from the fields of social psychology [30],game theory [36], and distributed AI [3, 23], reveals a significant level of agreementon the main stages involved in the process. We use this commonality to underpin ourgeneric negotiation model which is outlined below.2.1 A generic model of negotiationNegotiation is a process that takes place between two or more agents who are at-tempting to achieve goals which they cannot, or prefer not to, achieve on their own.These goals may conflict, in which case the agents have to bargain about which agentAgents that Reason and Negotiate by Arguing 263achieves which goal, or the agents may depend upon