Planning with PDDL3 Qualitative Constraints for Cost-Optimal Solutions Through Compilation

We study the problem of finding cost-optimal solutions to planning problems that feature qualitative state trajectory constraints expressed in PDDL3. These constraints are properties that every plan must satisfy and can be seen as a fragment of LTL over finite traces. The state-of-the-art system for handling PDDL3 problems is a compilation-based approach. Such a compilation has been tested only using a satisficing planner, while the case where we require the planner to find optimal solutions is scarcely studied; with this paper, we want to fill this gap. We propose an experimental analysis that involves TCORE, the current state-of-the-art compilation approach to handle qualitative PDDL3 constraints, and two compilation approaches supporting arbitrary LTL formulas. We evaluate each system using two optimal planners, and we analyze the results using different metrics to explain the behavior of the considered approaches. Our analysis confirms the result previously obtained with a suboptimal planner; that is, in the optimal setting TCORE outperforms all other compilations over our benchmark domains.