Oo-line Reasoning for On-line Eeciency: Knowledge Bases

The complexity of reasoning is a fundamental issue in AI. In many cases, the fact that an intelligent system needs to perform reasoning on-line contributes to the diiculty of this reasoning. This paper considers the case in which an intelligent system computes whether a query is entailed by the system's knowledge base. It investigates how an initial phase of oo-line preprocessing and design can improve the on-line complexity considerably. The notion of an eecient basis for a query language is presented, and it is shown that oo-line prepro-cessing can be very eeective for query languages that have an eecient basis. The usefulness of this notion is illustrated by showing that a fairly expressive language has an eecient basis. A dual notion of an eecient disjunctive basis for a knowledge base is introduced, and it is shown that oo-line preprocessing is worthwhile for knowledge bases that have an eecient disjunctive basis.