A Temporal Planning System for Level 3 Durative Actions of PDDL+

Many planning domains have temporal features that can be expressed as durations associated with actions. Unfortunately, the conservative model of actions of most temporal planners is not appropriate for some domains which require richer models. Level 3 of PDDL2.1 introduces a model of durative actions which includes local conditions and effects to be satisfied at different times during the execution of the actions, thereby giving the planner freedom to plan concurrent actions. This paper presents a temporal planning system (TPSYS), which combines the ideas of Graphplan and TGP, to plan with such durative actions. The approach necessitates the modification of some aspects of the basic planning algorithm: the mutex reasoning, the generation of the temporal graph and the search for an optimal plan. Although the algorithm becomes more complex, the experimental results demonstrate it remains feasible as a way to deal with durative actions.