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Coordination as Negotiated Transactions

Jean-Marc Andreoli
Usually, task coordination systems distinguish several aspects of task execution: the functional aspect is concerned by what tasks are to be performed by the system. The behavioral aspect concerns when particular tasks are to be executed. The technological aspect concerns how tasks are actually performed. Coordination systems generally do not provide any tools to support the technological aspect; instead, they are open systems which can (or have the ambition to) interoperate with various other systems and platforms which implement the actual actions. Abstracting the "how" part of activities from the "what" and "when" make coordination particularly amenable to the declarative kind of specifications offered by rule-based frameworks. Working out which tasks have to be done (the "what" part) often requires a negotiation between the coordinator and the external systems which are supposed to then perform the tasks; as for sequentializing the tasks in an appropriate order (the "when" part), it requires some form of synchronization. We claim that these two aspects, negotiation and synchronization, can be elegantly supported in a rule-based framework by two mechanisms which, in the past, have been successfully integrated with rules: respectively, constraint propagation (and solving) and transactions. We propose a rule based coordination framework where negotiation and synchronization aspects are specified in terms of, respectively, constraint solving, and transactions.
Freitag, Jones, Lengauer and Schek (Eds): Object Orientation with Parallelism and Persistence, Kluwer Academic Publishers, 1996.


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