Liveness and Fairness Properties in Multi-Agent Systems
چکیده
Problems of liveness and fairness are considered in multi-agent systems by means of abstract languages. Different approaches to define such properties for the agents and for a multi-agent system as a whole are discussed. It turns out that the properties of a multi-agent system need not correspond to separately de-finable properties of the agents (e.g. a community of fair agents need not constitute a fair multi-agent system). In general, analysis and verification need the consideration of the whole system, and the agents have to be considered in the context of the system, too. The results are not unique, there are different results for deadlock freedom, liveness and fairness, respectively. 1 Introduction Problems of liveness and fairness have been studied intensively for concurrent systems. But related considerations are missing for multi-agent systems nevertheless they have been inquired e.g. already in [Bond and Gasser, 1988]. This does not mean that there are no attempts to reach fairness conditions in the multi-agent systems (e.g. by scheduling), but there is also a need to consider general problems of liveness and fairness for such systems. This paper is an attempt to fill this gap from a view point of abstract languages. A first problem is the definition of deadlock-free, live or fair agents, respectively, and of deadlock-free, live or fair multi-agent systems. The next problem is the relationship between e.g. fair multi-agent systems and fair agents. Are the properties of a multi-agent system given by the properties of its agents, does a community of fair agents constitute a fair system? The last question is also of interest with respect to the analysis and verification of multi-agent systems. If the properties of a system are determined by its components, then the analysis can be done by analysing these components. But a real benefit is given only if the component analysis can be done separately for each component without regarding the whole system. The latter implies that it must be possible to define the properties of the agents "locally" without "globally" referring to the whole system. In the paper, we shall introduce two approaches to the definition of properties for the agents in a multi-agent system. The "local" one fulfills this restriction but may be sometimes misleading with respect to the intuitive meaning of the properties we want to define. The "global" one on the other hand may sometimes better reflect the intuitive meanings, but it needs …