Temporal Reasoning in the SIPE-2 Planner

This paper describes a project that added temporal information and constraints to SRI International’s SIPE–2 hierarchical, nonlinear planning system. The goal was to incorporate the ability to represent temporal relationships between actions within a plan, and time window constraints on individual actions, and to maintain these constraints during the planning process. The extensions described in this paper were added as a “temporal plan critic” that checks the temporal constraints at the end of each planning level. This project was the initial phase of a Technology Integration Experiment (TIE) undertaken as part of the DARPA/Rome Laboratory Planning Initiative to explore the integration of temporal reasoning into planning systems. The TIE involves researchers from SRI, GE, and Honeywell. Integrating temporal reasoning into planning systems is an important area of research, since many domains contain temporal constraints that must be represented in order for planning to be successful. The work described in this paper is a relatively small-scale effort that lays the groundwork for a more complete integration of temporal reasoning capabilities into SIPE–2. The rest of this paper is organized as follows: Section 2 describes SIPE–2 and SOCAP, the application that was used as the domain for implementation and testing. Section 3 describes the current temporal reasoning capabilities of SIPE–2. Section 4 describes the methods we implemented for representing and maintaining temporal information in SIPE–2 plans. Section 5 presents our results and the status of the TIE. Section 6 presents related work on the use of temporal reasoning in planning, and Section 7 describes open problems, future work, and conclusions.