The theme of this thesis is "metaphor-based negotiation". By metaphor-based negotiation I mean a category of approaches for problem-solving in Distributed Artificial
Intelligence (DAI) that mimic some aspects of human negotiation behaviour. The
research in this dissertation is divided into two closely related parts. Cooperative interaction among agents in a multiagent system (MAS) is discussed in general, and
the discussion leads to a formal definition of metaphor-based negotiation. Then, as
a specific application, a "spring-based" computational model for metaphor-based negotiation is developed as an approach to solving movement planning, specifically the
AGV scheduling problem (AGVSP) — determing the timings of AGVs' activities, of
automated guided vehicles (AGVs) in a factory.By formally addressing the multi-agent cooperative interaction problem and assuming
that agents in a MAS are rational, benevolent and fully informed, an initial strategy
set of cooperative interaction can be reduced to a strategy set by eliminating strategies
that are irrational in a group sense. However, it is proved in this dissertation that, in
the remaining strategy set, no unique strategy can be found that is acceptable to all
agents according their individual preferences. More specifically, in this smaller strategy
set, if one agent moves from one strategy to another in an attempt to better its individual goal achievement, then there is at least one agent whose goal achievement will
be negatively affected by such a move. So, the cooperative interaction problem can
only be partially solved if no further knowledge is given to those agents. The idea of a
common sense principle is introduced in this dissertation to overcome the deficiencies
of the assumptions of rationality, benevolence and full-informedness.In reality, the assumption of full-informedness of agents may not be practical. Communication is needed for agents to (1) exchange their local problem solving information,
and (2) exchange proposals for global problem solving, when their views are in conflict.
Based on the discussion of cooperative interaction, a formal definition of metaphorbased
negotiation is proposed to formally indicate what is a proposal and what is the
condition for accepting a proposal from another agent. In this definition, the common
sense principle is one of the most important features, not found in definitions of negotiation available so far in the literature, which guides agents to find an agreement
when negotiation is running into difficulties.The AGVSP involves timing activities for each AGV in a AGV-based factory. The
AGVSP is naturally distributed: the whole problem can be easily divided into several
subproblems each of which involves timing of activities of one AGV. Therefore, it is
intuitively straightforward for us to seek DAI approaches to solving the AGVSP. In
spired by Kwa's Iterative Negotiation Model [Kwa 88b] [Kwa 88a] for the AGVSP, we
developed a spring-based (metaphor-based) negotiation model for the AGVSP to overcome some vital problems in Kwa's model. The idea of the spring-based negotiation
model is described below:The AGVSP can be regarded as a Distributed Constraint Satisfaction Problem (DCSP)
and solved in a MAS. Each agent in the MAS is designed to solve a subproblem — a
local scheduling problem which is a small Constraint Satisfaction Problem (CSP). Conflicts exist when intra-agent constraints or inter-agent constraints are violated. These
constraints can be classified into hard constraints— those that can not be relaxed at
the agent level unless the system designer permits (e.g., by providing an arbitrator),
and soft constraints — those that can be relaxed at the agent level when necessary.
When agents are in conflict, i.e, when some inter-agent constraints are violated (or
say, when one agent's timings of its activities overlap those of some other agents),
these agents involved will resolve the conflicts through a (metaphor-based) negotiation
procedure in which conflicts will be gradually resolved by each agent's relaxation of
its intra-agent constraints, i.e, by yielding some amount of its initially allocated resources to other agents or by shifting its initially allocated resources. The negotiation
can be viewed as a process of exchanging proposals (of cooperative strategies) between
conflicting agents, where a cooperative strategy is a possible resolution to a conflict
according to the viewpoint of the proposing agent. However, since agents are designed
to be rational, each agent that is involved in the conflicts will try hard to relax its
intra-agent constraints as little as possible. Further, it is reasonably acceptable that
the more an intra-agent constraint has been relaxed the less the respective agent is
willing to relax it further. This feature can be modeled by a spring — the more it
has been compressed the harder it is to compress it further. Based on this inspiration,
a spring-based computational model of metaphor-based negotiation is proposed: each
agent's local schedule is represented by a local spring network in which each spring element represents a soft intra-agent constraint. Relaxation of an intra-agent constraint
is likened to a spring being compressed by external forces from other agents. As a
consequence, the compressed spring will also show a reacting force upon those compressing agents. An agreement will be reached when those forces and reacting forces
are balanced. This is the common sense principle in the spring-based negotiation. The
model solves some key issues, e.g., how to select negotiation techniques and skills during the process of negotiation, that have not been solved by Kwa's iterative negotiation
model. Some experimental evidence of the value of this model is presented
