PDDL2.1: An Extension to PDDL for Expressing Temporal Planning Domains
  In recent years research in the planning community has moved increasingly
toward s application of planners to realistic problems involving both time and
many typ es of resources. For example, interest in planning demonstrated by the
space res earch community has inspired work in observation scheduling,
planetary rover ex ploration and spacecraft control domains. Other temporal and
resource-intensive domains including logistics planning, plant control and
manufacturing have also helped to focus the community on the modelling and
reasoning issues that must be confronted to make planning technology meet the
challenges of application. The International Planning Competitions have acted
as an important motivating fo rce behind the progress that has been made in
planning since 1998. The third com petition (held in 2002) set the planning
community the challenge of handling tim e and numeric resources. This
necessitated the development of a modelling langua ge capable of expressing
temporal and numeric properties of planning domains. In this paper we describe
the language, PDDL2.1, that was used in the competition. We describe the syntax
of the language, its formal semantics and the validation of concurrent plans.
We observe that PDDL2.1 has considerable modelling power --- exceeding the
capabilities of current planning technology --- and presents a number of
important challenges to the research community.
