Planning with Sharable Resource Constraints

When planning systems deal with realistic domains , they must cope with a large variety of constraints imposed by the environment such as temporal or resource constraints The ro-bustness of the generated plan is a direct consequence of a correct handling of these constraints We argue that increasing the expres-siveness of a representation can be achieved without fundamentally affecting the global efficiency of the search This paper presents a temporal planner, LxTeT, which integrates sharable resource management into the process of plan generation In IxTeT, planning operators are described as temporal structures of conditions, effects and sharable resource uses During the search, pending subgoals, protection threats and resource conflicts are detected by three flaw analysis modules The detection of sharable resource conflicts is performed thanks to an efficient clique-search algorithm on a possible intersection graph The control of the search is based on a least-commitment opportunistic strategy Our approach has been implemented, tested and shown to be satisfactory in various application domains 1 Introduction Classical approaches decompose plan generation and resource management into two different steps for solving a given planning problem Plan generation consists in selecting and organising a set of operators that will achieve the problem goals, its result is a plan, that is a partially ordered set of operators Resource management is then performed on this plan to ensure its correctness with respect to temporal and resource constraints The result, then, is a schedule that, if executed, will ensure the goal resolution while satisfying the physical constraints of the environment The strict separation between plan generation and re source management raises difficulties such as how to backtrack to the plan generation process, when necessary , or how to generate the plan in an opportunistic way according to resource constraints This paper develops a representation and an algorith-mic approach integrated into a system called IxTeT, for handling abreast and in an opportunistic way plan generation and time/resource management The following section is a short digest of scheduling and planning literature that influenced our work Section 3 describes a temporal representation of operators and problems The genera] control of the planner is discussed m section 4 whereas section 5 focuses on the resource analysis module We finally presents some experimental results and applicability domains for our system 2 Related Work 2 1 Scheduling Scheduling systems are essentially concerned with time and resource management ISIS [Fox and Smith, 1984] was …