IJCAI'77 Proceedings of the 5th international joint conference on Artificial intelligence - Volume 2
Planning using a temporal world model
IJCAI'83 Proceedings of the Eighth international joint conference on Artificial intelligence - Volume 2
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In a temporal planning and reasoning system, many logical assertions will have a limited life span: they are "terminated" by later, contradictory assertions. By observing assertion terminators, the lifetime of an assertion can be bounded within an interval called the scope. Assertion scopes can greatly reduce the number of relevant matches returned from an assertion database. Scopes and terminators also permit the more efficient determination of contemporaneous assertions for forward chaining of event rules. Window cutoff is an execution time accelerator for determining if two activities are ordered in a plan, a high frequency, utility operation in plan synthesis. The acceleration is accomplished by doing an early cutoff of search paths to the "lower" activity based on time constraints. These mechanisms reduced the execution time of a temporal planner called DEVISER by four orders of magnitude for 70 goals, allowing very long planning problems to be solved. The mechanisms described employ time constraints to accelerate planning, and are not applicable to precedence planners. DEVISER is a performance planner which has been applied experimentally in planning activities for the Voyager spacecraft in its encounter with Uranus in 1986.