Joshua: Uniform Access to Heterogeneous Knowledge Structures, or Why Joshing Is Better than Conniving or Planning

Abstract

This paper presents Joshua, a system which provides syntactically uniform access to heterogeneously implemented knowledge bases. Its power comes from the observation that there is a Protocol of Inference consisting of a small set of abstract actions, each of which can be implemented in many ways. We use the object-oriented programming facilities of Flavors to control the choice of implementation. A statement is an instance of a class identified with its predicate. The steps of the protocol are implemented by methods inherited from the classes. Inheritance of protocol methods is a compile-time operation, leading to very fine-grained control with little run-time cost. Joshua has two major advantages: First, a Joshua programmer can easily change his program to use more efficient data structures without changing the rule set or other knowledge-level structures. We show how we thus sped up one application by a factor of 3. Second, it is straightforward to build an interface which incorporates an existing tool into Joshua, without modifying the tool. We show how a different TMS, implemented for another system, was thus Interfaced to Joshua.