Planning in time: windows and durations for activities and goals

A general purpose automated planner/scheduler is described which generates parallel plans to achieve goals with imposed time con-straints. Both durations and start time windows may be specified for sets of goal conditions. The parallel plans consist of not just actions but also of events (triggered by circumstances), inferences, and scheduled events (completely beyond the actor's control). Deterministic dura-tions of all such activities are explicitly modeled, and may be any com-putable function of the activity variables. A start time window for each activity in the plan is updated dynamically during plan generation, in order to maintain consistency with the windows and durations of adja-cent activities and goals. The plans are tailored around scheduled events. The final plan network resembles a PERT chart. From this a schedule of nominal start times for each activity is generated. Ex-amples are drawn from the traditional blocksworld and also from a real-istic ``Spaceworld,'' in which an autonomous spacecraft photographs objects in deep space and transmits the information to Earth. The author is with the Information Systems Research Section, Jet Propulsion Laboratory, Pasadena, CA 91109.