Storing and Evaluating Horn-Clause Rules in a Relational Database

This paper describes a practical approach to storing and evaluating Horn-clause rules in a relational database system. The intention is to give a complete outline of what needs to be added to an existing relational database system to allow it to support full logic programming functions. Implementation issues for each new function are discussed. We show how Horn-clause rules can be translated into database commands without recourse to semantics and how their evaluation can be performed in the database itself. This brings the complete logic programming environment within reach of the database management system, allowing data and rule sharing, concurrency control, recovery procedures, etc., to be used. New is that the complete logic programming environment is incorporated into the database system. IBM Business System 12, extended in this way, may be a suitable vehicle for expert system applications. Copying in printed form for private use is permitted without payment of royalty provided that (1) each reproduction is done without alteration and (2) the Journal reference and IBM copyright notice are included on the first page. The title and abstract, but no other portions, of this paper may be copied or distributed royalty free without further permission by computer-based and other information-service systems. Permission to republish any other portion of this paper must be obtained from the Editor.