{\bf (Revision of CS-1991-42.)} The Near-Horn Approach to Disjunctive Logic Programming

This paper presents an overview of the near-Horn Prolog project at Duke University. The basic goal behind this project has been to extend Prolog to disjunctive logic programs (and thus full first-order expressibility) while retaining as much of the clarity and procedural simplicity of Prolog as possible. The approach taken to achieve this goal has been to combine Prolog with case analysis reasoning. The research work within the project can roughly be divided into three areas: procedure design, semantics, and implementation. Three different variants of Near-Horn Prolog have been devised, of which the most recent, Inheritance near-Horn Prolog (InH-Prolog), is the variant currently being favored. The semantics for the near-Horn Prologs, specifically for InH-Prolog, have been investigated, resulting in a case-analysis based fixpoint semantics which mimics the procedural behavior of InH-Prolog. Also, both classical and default negation have been incorporated into the near-Horn Prolog systems. Finally, an interpreter for the original near-Horn Prolog variant has been implemented, and a compiler for the InH-Prolog variant is currently nearing completion.