Admissible Makespan Estimates for PDDL2.1 Temporal Planning

Though recent renewed interest in “expressive” temporal planning, as exemplified by PDDL2.1, has led to advances, few such planners to date can guarantee optimality, or even bounded suboptimality, w.r.t. plan makespan. As a step towards improving planners’ awareness of the quality of their plans, we describe three ways of obtaining lower bound functions, i.e., admissible heuristics, for plan makespan for PDDL2.1 problems. Two directly make use of heuristics for other planning models (conservative temporal and additive cost planning), thus enabling PDDL2.1 planners to take advantage of current and future developments of such heuristics.