Reference: Heckerman, D.; Horvitz, E. J.; & Nathwani, B. N. Toward Normative Expert Systems: The Pathfinder Project. KSL, February, 1990.
Abstract: We describe key issues and achievements on the Pathfinder expert-system project. Pathfinder research has extended over 5 years at the University of Southern California and at Stanford University. Our investigation of automated reasoning has spanned several paradigms for representing and reasoning with expert medical knowledge. The Pathfinder team has concentrated on the construction of normative expert systems, which are expert systems based on the principles of decision theory. Within the normative paradigm, we have developed useful techniques for acquiring, representing, manipulating, and explaining complex medical knowledge. A large component of such knowledge is made available only through careful assessment of subjective probabilistic relationships. Although the bulk of Pathfinder research has been carried out within the domain of lymph-node pathology, the insights and techniques have relevance to a wide variety of complex biomedical domains. We introduce the project, describe the significance of normative reasoning in medicine, and review theoretical and empirical Pathfinder developments. We describe the techniques for constructing and managing a large probabilistic knowledge base, the use of a normative hypothetico-deductive architecture, the application of alternative information-acquisition strategies, the explanation of probabilistic inference, and the heuristic and normative evaluation of the Pathfinder reasoning system.