This paper investigates workflow systems in which the enactment and completion of activities have to satisfy a set of quantitative temporal constraints. Different activities are usually performed by autonomous agents, and the scheduling of activities by the enactment service has among its goals the minimization of communication and synchronization among the agents. The paper formally defines the notion of a schedule for these workflow systems and its identifies a particularly useful class: free schedules. A schedule specifies a time range for the enactment, duration and completion of each activity in order to satisfy all the temporal constraints in the workflow. In a free schedule, an agent has to start its activity within the range specified in the schedule, but it is free to use any amount of time to finish the activity as long as it is between a minimum and maximum time he has declared when the workflow is designed. No synchronization with other agents is needed. The paper provides a method to characterize all the free schedules admitted by a workflow specification and an algorithm to derive them.
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