Layout of the Paper

In Section 4 we explain how PDDL+ builds on the foundations of the PDDL family of languages. We describe the syntactic elements that are new to PDDL+ and we remind the reader of the representation language used for expressing temporal plans in the family. We develop a detailed example of a domain, the battery power model of a planetary lander, in which continuous modelling is required to properly capture the behaviours with which a plan must interact. We complete this section with a formal proof showing that PDDL+ is strictly more expressive than PDDL2.1.

In Section 5 we explain why the theory of hybrid automata is relevant to our work, and we provide the key automaton constructs that we will use in the development of the semantics of PDDL+. In Section 6 we present the mapping from planning instances to HAs. In doing this we are using the syntactic constructs of the HA as our semantic model. In Section 7 we discuss the subset of HAs for which the Reachability problem is decidable, and why we might be interested in these models in the context of planning. We conclude the paper with a discussion of related work.