1987 年 2 巻 4 号 p. 492-500
PAL is an extended Prolog to deal with inheritance hierarchy (IH), which is a tree structure formed by the inclusion relation among classes and instances. It adopts class bound variables (CBVs), which are variables with class constraints. CBVs improve the inferential efficiency greatly by suppressing unnecessary backtracking and exhaustive searches <(2)>. In this paper we propose for IH Prolog two new techniques : IH compiler and IH clause indexing. IH compiler associates classes with intervals in order to reduce the ancestor-descendent relation of classes to the inclusion relation of intervals. This makes the unification of CBVs very efficient. IH clause indexing adopts class keys for hashing as well as instance keys which are commonly used in ordinary clause indexing, and enables PAL to avoid unnecessary tests of matching for clauses that do not satisfy class constraints of CBVs. These techniques are indispensable especially when we deal with large scale data bases, where much irrelevant knowledge interferes with fast inference. They can suppress the unnecessary information processing caused by such irrelevant knowledge, and can make the inference in the IH Prolog far more efficient.
