STRUCTURED PLANS WITH SHARING AND REPLICATION

This paper focuses on the issue of shared (vs. replicated) tasks in hi erarchical plan description. We extend the notion of task networks (or plan schemas) with constraint expressions, which determine which sub- plans may be shared among parent plans, which must be shared, and whic h must be replicated (that is, consist of disjoint events) in the plan schema. The semantics of constraint expressions are defined by using an intermediate, simplified, level of plans, and a base level of struc tured events (concrete, ''real-world'' events). Applications for this representation are in planning, plan recognition, and in databases of plans and schedules. In all these areas, the possibility of representi ng a large number of events with common structure compactly, provided by the plan schemas, is beneficial.