Relixpert — an expert system shell written in a database programming language

Abstract

We present an expert system shell for rule-based expert systems. The shell is written in less than 200 statement of Aldat and required eighteen person-days to design, code and test on a 100-rule expert system. Aldat is a programming language based on the relational algebra and partially implemented by the system relix. Relix is sufficient to run our expert system shell, relixpert, although some extensions to relix are suggested by our implementation. The expert system shell consists of editors for entering rule schemata, rules and facts, of consistency checkers for uniqueness and monotonicity of rules, and of an inference engine which can handle inequalities and ranges as well as equalities and which can do numerical computations. The principle result of this work is the ease with which the expert system shell was built in Aldat, a language intended for general database work, not for building expert systems. Another important result is the flexibility of the code: when it became apparent that monotonicity of rules is an important constraint, we were easily able to incorporate a checker into the system, which the commercial systems we were following are not able to do; generalization of simple inequalities to ranges and general boolean combinations of inequalities were not easy to do but also simplified the implementation. A final result is that the expert system shell has been implemented in a database language, thus making trivial the interface between an expert system and an extensive database.