Logic programming as a formalism for specification and implementation of computer systems

Abstract

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 of 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.