A hypothetical reasoning system is an important framework in the development of advanced knowledge-based systems. It can be effectively applied to many practical problems including model-based diagnosis, and designs. However, the inference speed of its prolog-based implementation is slow, and this is particularly because of inefficient backtracking. In order to overcome this problem, a fast hypothetical reasoning mechanism for propositional-logic knowlegde has been developed by combining the advantages of forward and backward reasoning styles. This fast mechanism, however, cannot be applied to hypothetical reasoning with predicate-logic knowledge where variables are included as arguments. The paper presents a fast hypothetical reasoning mechanism for predicate-logic knowledge as an extension of the above idea. A reasoning method developed in the deductive database area is effectively utilized to realize this fast mechanism, which can even manipulate recursive rules.
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