Question-asking strategies for Horn clause systems

An expert system applies the deduction rules in its knowledge base to a set of initial data to reach a conclusion. When the initial data are insufficient, the expert system may ask the user for additional information. This paper analyzes effectiveness and efficiency of question-asking strategies in expert systems with Horn clause knowledge bases. An effective strategy reaches a conclusion after asking as few questions as possible. An efficient strategy can be computed quickly. We prove that effective strategies are, unfortunately, not efficient. However, we present a somewhat less effective but very efficient strategy. It employs an algorithm which simultaneously performs deduction and question selection in log-linear time.