Declarative representation of strategic control knowledge

Strategic (control) knowledge typically specifies how a target task is solved. Representing such knowledge declaratively remains a difficult and practical knowledge engineering challenge. The key to addressing this challenge rests on two observations. One, strategic knowledge comprises two finer types of knowledge: subgoaling knowledge used to construct the goal structure for each problem situation pertaining to a target task, and goal-sequencing knowledge used to choose which subgoal in this goal structure is to be pursued at any given moment. Second, when subgoaling knowledge is explicit and expressed in declarative ontological terms, it is possible to fully express goal-sequencing knowledge in the same declarative terms. Building on these observations, we achieve three things. First, we analyse several conventional knowledge-based applications whose subgoaling and goal-sequencing knowledge is implicit, showing that making their subgoaling knowledge explicit permits (re)representing their goal-sequencing knowledge declaratively. Among the applications analysed are MORE and NEOMYCIN. Second, upon studying the roles of goal-sequencing knowledge vis-á-vis subgoaling knowledge, we develop a declarative formalism for representing goal-sequencing knowledge. Finally, we discuss and illustrate key benefits from using our declarative formalism, including an enhanced ability to validate and reuse goal-sequencing knowledge.