On Compiling Away PDDL3 Soft Trajectory Constraints without Using Automata

We address the problem of propositional planning extended with the class of soft temporally extended goals supported in PDDL3, also called qualitative preferences since IPC-5. Such preferences are useful to characterise plan quality by allowing the user to express certain soft constraints on the state trajectory of the desired solution plans. We propose and evaluate a compilation approach that extends previous work on compiling soft reachability goals and always goals to the full set of PDDL3 qualitative preferences. This approach directly compiles qualitative preferences into propositional planning without using automata to represent the trajectory constraints. Moreover, since no numeric fluent is used, it allows many existing STRIPS planners to immediately address planning with preferences without changing their algorithms or code. An experimental analysis presented in the paper evaluates the performance of state-of-the-art propositional planners using our compilation of qualitative preferences. The results indicate that the proposed approach is highly competitive with respect to current planners that natively support the considered class of preferences, as well as with a recent automata-based compilation approach.