Ordering Problem Subgoals

Most past research work on problem subgoal ordering are of a heuristic nature and very little attempt has been made to reveal the inherent relationship between subgoal ordering constraints and problem operator schemata. As a result, subgoal ordering strategies which have been developed tend to be either overly committed, imposing ordering on subgoals subjectively or randomly, or overly restricted, ordering subgoals only after a violation of ordering constraints becomes explicit during the development of a problem solution or plan. This paper proposes a new approach characterized by a formal representation of subgoal ordering constraints which makes explicit the relationship between the constraints and the problem operator schemata. Following this approach, it becomes straightforward to categorize various types of subgoal ordering constraints, to manipulate or extend the relational representation of the constraints, to systematically detect important subgoal ordering constraints from problem specifications, and to apply the detected constraints to multiple problem instances.