Formalism

In this section we present the syntactic foundations of PDDL+, clarifying how they extend the foregoing line of development of the PDDL family of languages. We rely on the definitions of the syntactic structures of PDDL2.1, which we call the Core Definitions. These were published in 2003 [Fox LongFox Long2003] but we repeat them in Appendix A for ease of reference.

PDDL+ includes the timed initial literal construct of PDDL2.2 (which provides a syntactically convenient way of expressing the class of events that can be predicted from the initial state). Although derived predicates are a powerful modelling concept, they have not so far been included in PDDL+. Further work is required to explore the relationship between derived predicates and the start-process-stop model and we do not consider this further in this paper.