Task Modeling with Reusable Problem-Solving Methods

Problem-solving methods for knowledge-based systems establish the behavior of such systems by de ning the roles in which domain knowledge is used and the ordering of inferences. Developers can compose problem-solving methods that accomplish complex application tasks from primitive, reusable methods. The key steps in this development approach are task analysis, method selection (from a library), and method con guration. Prot eg e-ii is a knowledge-engineering environment that allows developers to select and con gure problem-solving methods. In addition, prot eg e-ii generates domain-speci c knowledge-acquisition tools that domain specialists can use to create knowledge bases on which the methods may operate. The board-game method is a problem-solving method that de nes control knowledge for a class of tasks that developers can model in a highly speci c way. The method adopts a conceptual model of problem solving in which the solution space is construed as a \game board" on which the problem solver moves \playing pieces" according to prespeci ed rules. This familiar conceptual model simpli es the developer's cognitive demands when con guring the board-game method to support new application tasks. We compare con guration of the board-game method to that of a chronological-backtracking problem-solving method for the same application tasks (for example, Towers of Hanoi and the Sisyphus room-assignment problem). We also examine how method designers can specialize problem-solving methods by making ontological commitments to certain classes of tasks. We exemplify this technique by specializing the chronologicalbacktracking method to the board-game method.