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Working Together
behave towards its fellow team members. For example, if an agent drops its joint commitment because it believes that the goal will never be attained, then it is part of the notion of 'cooperativeness' that is inherent in joint action that it informs all of its fellow team members of its change of state. In this context, social conventions provide general guidelines, and a common frame of reference in which agents can work. By adopting a convention, every agent knows what is expected both of it, and of every other agent, as part of the collective worlung towards the goal, and knows that every other agent has a similar set of expectations. We can begin to define this lund of cooperation in the notion of a joint persistent goal (JPG),as defined in Levesque et al. (1990). In a JPG, a group of agents have a collective commitment to bringing about some goal q ;the motivation for t h s goal, i.e. the reason that the group has the commitment, is represented by Thus q might be 'move the heavy object', while + might be 'Michael wants the heavy object moved'. The mental state of the team of agents with this JPG might be described as follows:
+.
initially, every agent does not believe that the goal p is satisfied, but believes q is possible; every agent i then has a goal of p until the termination condition is satisfied (see below); until the termination condition is satisfied, then if any agent i believes that the goal is acheved, then it will have a goal that this becomes a mutual belief, and will retain this goal until the termination condition is satisfied; - if any agent i believes that the goal is impossible, then it will have a goal that this becomes a mutual belief, and will retain t h s goal until the termination condition is satisfied; - if any agent i believes that the motivation + for the goal is no longer present, then it will have a goal that this becomes a mutual belief, and will retain this goal until the termination condition is satisfied;
-
the termination condition is that it is mutually believed that either - the goal q is satisfied;
- the goal q is impossible to acheve; - the motivation/justification
+ for the goal is no longer present.
Commitments and conventions in ARCHON Jennings (1993a, 1995) investigated the use of commitments and such as JPGs in the coordination of an industrial control system called ARCHON (Wittig, 1992;Jennings et al., 1996a; Perriolat et al., 1996).He noted that commitments and conventions could be encoded as rules in a rule-based system. T h s makes it possible to explicitly encode coordination structures in the reasoning mechanism of an agent.