Logical levels of problem solving

This paper demonstrates how clear, efficient problem solving programs can be written within logic programming. The key point is the consideration of levels involved, both in the problem solving itself and in the underlying logic. Three levels of knowledge necessary for intelligent problem solving are identified-a level of domain knowledge, a level of methods and strategies, and a planning level. The approach introduced here relates these levels to the distinction between object and meta languages. Two classes of programs are presented. First, single level problem solvers are introduced. These are at the methods level and constitute a meta language of the problem domain. Second, flexible multilevel problem solvers are outlined which can be built as extensions of the single level programs