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 specification includes a language syntax, a proof (or query evaluation) procedure, a description of the language's semantics, and a specification of the relationships between assertions, queries, and application databases. DLOG's data description language is the Horn clause subset of first order logic [Kowalski79, Kowalski81], augmented with descriptive terms and non-Horn integrity constraints. The descriptive terms are motivated by AI representation language ideas, specifically, the descriptive terms of the KRL language [Bobrow77]. A similar facility based on logical descriptions is provided in DLOG. DLOG permits the use of definite and indefinite descriptions of individuals and sets in queries and assertions. The meaning of DLOG's extended language is specified as Horn clauses that describe the relation between the basic language and the extensions. The experimental implementation is a 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 procedure (cf. LOGLISP [Robinson82]). The experimental system includes Prolog 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 knowledge base management system is exercised by describing an undergraduate degree program. The example application is a description of the Bachelor of Computer Science degree requirements at The University of British Columbia. This application demonstrates how DLOG's descriptive terms provide a concise description of degree program knowledge, and how that knowledge is used to specify student programs and select program options. / Science, Faculty of / Computer Science, Department of / Graduate

The expressive power of logic-programming languages allows utilization of conventional constructs in development of computer systems based on logic programming. However, logic-programming languages have many novel features and capabilities. This thesis investigates how advantage can be taken of these features in the development of a logic-based computer system. It demonstrates that innovative approaches to software, hardware, and computer system design and implementation are feasible in a logic-programming context and often preferable to adaptation of conventional ones. The investigation centers on three main ideas: executable specification, declarative I/O, and implementation through transformation and meta-interpretation. A particular class of languages supporting parallel computation, committed-choice logic-programming languages, are emphasized. One member of this class, Concurrent Prolog, serves as the machine, specification, and implementation language. The investigation has several facets. Hardware, software, and overall system models for a logic-based computer are determined and examined. The models are described by logic programs. The computer system is represented as a goal for resolution. The clauses involved in the subsequent reduction steps constitute its specification. The same clauses also describe the manner in which the computer system is initiated. Frameworks are given for developing models of peripheral devices whose actions and interactions can be declaratively expressed. Interactions do not rely on side-effects or destructive assignment, and are term-based. A methodology is presented for realizing (prototypic) implementations from device specifications. The methodology is based on source-to-source transformation and meta-interpretation. A magnetic disk memory is used as a representative example, resulting in an innovative approach to secondary storage in a logic-programming environment. Building on these accomplishments, a file system for a logic-based computer system is developed. The file system follows a simple model and supports term-based, declarative I/O. Throughout the thesis, features of the logic-programming paradigm are demonstrated and exploited. Interesting and innovative concepts established include: device processes and device processors; restartable and perpetual devices and systems; peripheral devices modelled as function computations or independent logical (inference) systems; unique, compact representations of terms; lazy term expansion; files systems as perpetual processes maintaining local states; and term- and unification-based file abstractions. Logic programs are the sole formalism for specifications and implementations. / Science, Faculty of / Computer Science, Department of / Graduate