Argumentation has proved a useful tool in defining formal semantics for assumption-based reasoning by viewing a proof as a process in which proponents and opponents attack each others arguments by undercuts (attack to an argument's premise) and rebuts (attack to an argument's conclusion). In this paper, we formulate a variety of notions of attack for extended logic programs from combinations of undercuts and rebuts and define a general hierarchy of argumentation semantics parameterised by the notions of attack chosen by proponent and opponent. We prove the equivalence and subset relationships between the semantics and examine some essential properties concerning consistency and the coherence principle, which relates default negation and explicit negation. Most significantly, we place existing semantics put forward in the literature in our hierarchy and identify a particular argumentation semantics for which we prove equivalence to the paraconsistent well-founded semantics with explicit negation, WFSX @math . Finally, we present a general proof theory, based on dialogue trees, and show that it is sound and complete with respect to the argumentation semantics.
The need for negotiation in multi-agent systems stems from the requirement for agents to solve the problems posed by their interdependence upon one another. Ne- gotiation provides a solution to these problems by giv- ing the agents the means to resolve their conflicting objectives, correct inconsistencies in their knowledge of other agents' world view, and coordinate a joint ap- proach to domain tasks which benefits all the agents concerned. We propose a framework, based upon a system of argumentation, which permits agents to ne- gotiate to establish acceptable ways to solve problems. offer concessions, and (hopefully) come to a mutually acceptable agreement--in other words to negotiate. This paper presents a well-grounded framework for describing the reasoning process of negotiating agents. This framework is based upon a system of argumenta- tion which may be used both at the level of all agent's internal reasoning and at the level of negotiation be- tween agents. An originating agent puts forward an initial proposal. The recipient agents evaluate the pro- posal by constructing arguments for and against it. If the proposal is unacceptable, the recipient constructs an argument against the initial proposal or in favour of a new alternative. This process continues until a proposal or counter-proposal is acceptable to all the parties involved or until the negotiation breaks down without an agreement. This paper presents a formal model covering the essence of the negotiation process which can be spe- cialised to describe specific strategies and tactics, all integrated framework for assessing proposals and for generating appropriate counter-proposals, and an in- tuitively appealing way of conducting reasoning and negotiation in the presence of imprecise and missing information.   The need for negotiation in multi-agent systems stems from the requirement for agents to solve the problems posed by their interdependence upon one another. Negotiation provides a solution to these problems by giving the agents the means to resolve their conflicting objectives, corect inconsistencies in their knowledge of other agents' world views, and coordinate a joint approach to domain tasks which benefits all the agents concerned. We propose a framework, based upon a system of argumentation, which permits agents to negotiate in order to establish acceptable ways of solving problems. The framework provides a formal model of argumentation-based reasoning and negotiation, details a design philosophy which ensures a clear link between the formal model and its practical instantiation, and describes a case study of this relationship for a particular class of architectures (namely those for belief-desire-intention agents). Dialogue represents a powerful means to solve problems using agents that have an explicit knowledge representation, and exhibit a goal-oriented behaviour. In recent years, computational logic gave a relevant contribution to the development of Multi-Agent Systems, showing that a logic-based formalism can be effectively used to model and implement the agent knowledge, reasoning, and interactions, and can be used to generate dialogues among agents and to prove properties such as termination and success. In this paper, we discuss the meaning of termination in agent dialogue, and identify a trade-off between ensuring dialogue termination, and therefore robustness in the agent system, and achieving completeness in problem solving. Then, building on an existing negotiation framework, where dialogues are obtained as a product of the combination of the reasoning activity of two agents on a logic program, we define a syntactic transformation of existing agent programs, with the purpose to ensure termination in the negotiation process. We show how such transformations can make existing agent systems more robust against possible situations of non-terminating dialogues, while reducing the class of reachable solutions in a specific application domain, that of resource reallocation. In a multi-agent environment, where self-motivated agents try to pursue their own goals, cooperation cannot be taken for granted. Cooperation must be planned for and achieved through communication and negotiation. We present a logical model of the mental states of the agents based on a representation of their beliefs, desires, intentions, and goals. We present argumentation as an iterative process emerging from exchanges among agents to persuade each other and bring about a change in intentions. We look at argumentation as a mechanism for achieving cooperation and agreements. Using categories identified from human multi-agent negotiation, we demonstrate how the logic can be used to specify argument formulation and evaluation. We also illustrate how the developed logic can be used to describe different types of agents. Furthermore, we present a general Automated Negotiation Agent which we implemented, based on the logical model. Using this system, a user can analyze and explore different methods to negotiate and argue in a noncooperative environment where no centralized mechanism for coordination exists. The development of negotiating agents in the framework of the Automated Negotiation Agent is illustrated with an example where the agents plan, act, and resolve conflicts via negotiation in a Blocks World environment. Many autonomous agents operate in domains in which the cooperation of their fellow agents cannot be guaranteed. In such domains negotiation is essential to persuade others of the value of co-operation. This paper describes a general framework for negotiation in which agents exchange proposals backed by arguments which summarise the reasons why the proposals should be accepted. The argumentation is persuasive because the exchanges are able to alter the mental state of the agents involved. The framework is inspired by our work in the domain of business process management and is explained using examples from that domain. The ability to view extended logic programs as argumentation systems opens the way for the use of this language in formalizing communication among reasoning computing agents in a distributed framework. In this paper we define an argumentative and cooperative multi-agent framework, introducing credulous and sceptical conclusions. We also present an algorithm for inference and show how the agents can have more credulous or sceptical conclusions.