Integrating the planning and scheduling of relatively independent tasks can greatly improve the feasibility of achieving all the tasks in a timely manner. This paper investigates a tightly coupled but separated planning and scheduling system. This planning-scheduling system takes a large number of high-level goals and plans them out in a serial fashion. However, before committing to a plan for a particular goal, the planning system queries the scheduling system to check for the feasibility of achieving the plan's goal given the current state and all the commitments made for previous plans. Given a finite set of resources and enough plans that use those resources, the scheduling system must reply that some of the plans are infeasible. How the planning system responds to such an infeasible reply, and how these responses affect how to achieve the plans is the subject of this paper.
The general approach to handling infeasible replies, is to search two different sources of knowledge: the knowledge about recovering from scheduling problems by fixing the schedule, and the planning knowledge about alternative plans. At this time Wed Aug 21 12:18:24 EDT 1996 we don't know the tradeoffs between which knowldege source to search.