A logic data model for the machine representation of knowledge

Abstract

DLOG is a logic-based data model developed to show how logic-programming can combine contributions of Data Base Management (DBM) and Artificial Intelligence (AI). The DLOG data model is based on a logical formulation that is a superset of the relation data model Reiter83 , and uses Bowen and Kowalski's notion of an amalgamated meta and object language Bowen82 to describe the relationship between data model objects. The DLOG specification includes a language syntax, a proof (or query evalution) procedure, a description of the language's semantics, and a specification of the relationships between assertions, queries, and application databases. DLOG's basic data description language is the Horn clause subset of first order logic Kowalski79, Kowalski81 , together with embedded descriptive terms and non-Horn integrity constraints. The embedded terms are motivated by Artificial Intelligence representation language ideas, specifically, the descriptive terms of the KRL language Bobrow77 . A similar facility based on logical descriptions is provided in DLOG. The DLOG language permits the use of definite and indefinite descriptions of individuals and sets in both queries and assertions. The meaning of DLOG's extended language is specified by writing Horn clauses that describe the relation between the basic language and the extensions. The experimental implementation is the appropriate Prolog program derived from that specification. The DLOG implementation relies on an extension to the standard Prolog proof procedure. This includes a unification procedure that matches embedded terms by recursively invoking the DLOG proof proceudre (ef. LOGLISP Robinson82 ). The experimental system includes logic-based implementations of traditional database facilities (e.g., transactions, integrity constraints, data dictionaries, data manipulation language facilities), and an idea for using logic as the basis for heuristic interpretation of queries. This heuristic uses a notion of partial match or sub-proof to produce assumptions under which plausible query answers can be derived. The experimental DLOG database (or base) management system is exercised by describing an undergraduate degree program. The example application database is a description of the Bachelor of Computer Science degree requirements at The University of British Columbia. This application demonstrates how DLOG's embedded terms provide a concise description of degree program knowledge, and how that knowledge is used to specify student programs, and select program options.