IxTeT: an integrated approach for plan generation and scheduling

In a traditional approach to solve complex planning problems, plan generation and scheduling are addressed at two different steps of the resolution: plan generation answers the question “what to do?” and scheduling, the question “how to do it?”. This paper describes a planning system, called IxTeT, that handles together and in an opportunistic way plan generation and scheduling, on the basis that the two questions are very much interdependent. Thanks to a rich formalism to represent time, resources, state of the world and changes, our planning system can address a large panel of realistic problems. The search relies on the resolution of flaws on the current plan: it is controlled by a least-commitment opportunistic strategy coupled with an original abstraction hierarchy. A heuristic search driven by a near-admissible algorithm ensures at the same time the global efficiency of the system and the good quality of the solution in terms of flexibility