Durative Planning in HTNs

This paper provides techniques for hierarchical task network (HTN) planning with durative actions. HTNs can provide useful heuristic guidance to planners, express goals that cannot be expressed in simple first principles planners, and allow plan generation to be limited by external constraints. The decomposition information in HTN plans can also help guide plan execution. This paper provides a method for encoding PDDL Level 3 durative actions in an HTN formalism compatible with the SHOP2 planner. Efficient planning with these actions requires additional search control. We illustrate the utility of the technique with experimental results on the IPC 2004 AIRPORT domain, and explain how SHOP2 methods were written for this domain.