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Coordination Services

 

Interagents offer the coordination level required by agents to cooperate in non-trivial ways. An interagent allows interdependencies between agents' communicative acts to be ordered. These interdependencies can be defined declaratively inside each interagent by means of a conversation protocol. A conversation protocol represents the conventions adopted by agents when interacting through the exchange of messages. A conversation protocol can also be seen as a an agent's plan to achieve some goal[6]. We model and implement conversation protocols as a special type of pushdown automaton. Pushdown automata, unlike finite state machines, allow context to be stored and to be subsequently retrieved for an ongoing conversation.

Conceptually, we have decomposed a conversation protocol into (see Figure 2):

 

  figure110


Figure: Conversation protocol for the foreign evaluation capability of Plural [12]. The conversation protocol followed by Plural agents during a foreign evaluation is modelled and implemented in an interagent as a pushdown automaton tex2html_wrap630 such that: tex2html_wrap631 . Messages followed by / stand for performatives sent by the interagent's user, whilst messages preceded by / stand for performatives received by the interagent's user.

Formally, a conversation protocol, like a pushdown automaton [4], is a 7-tuple :

displaymath661

where

Messages queued by interagents can queue-jump only if they produce a transition in the conversation protocol. Therefore, in certain way interagents constrain what an agent can utter and hear, and when. For instance, Figure 2 shows instantiation c-87 of a conversation held by agents A and B. The following transition:

displaymath662

indicates in such conversation protocol that when:

then the following move

displaymath663

takes place in the finite state control. As a result, conversation c-87 switches to state tex2html_wrap644 , the corresponding message is extracted from the input list and forwarded to the corresponding addressee, and the message on the top of the pushdown list is popped out.




next up previous
Next: Conversation Protocol Definition Up: JIM A Java Previous: Communication Services

Francisco Martin
Wed Sep 9 13:33:33 MET DST 1998