A top-down language analyzer

Abstract

Parsing is the process which matches a given input against prestored possibilities (a grammar) to discover the structure of acceptable candidates. It is relevant to both natural and artificial languages--both English and command or query languages. Although parsing is necessary to computer processing of all languages, and the parser described in this paper (PARSYN) is a general-purpose top-down parser, the focus of this paper is its applicability as a computationally efficient processor of natural language. In natural language, a grammar is taken to cover a subset of the language; parsing proceeds both top-down looking for constituents and bottom-up replacing the words by syntactic categories for processing. Since procedural formulation is equivalent to an ATN, complete computational coverage of all natural language parsers can be obtained with template processing and an ATN. PARSYN is a computational accelerator for parsing which provides this coverage. The algorithm of PARSYN is a Recursive Transition Network (RTN) with interrupt capability; the combination can serve as an ATN or template processor. Yet, PARSYN is simple enough to be attached to a microprocessor based English-language processing system ( — BE—, “microBE”, for micro-processor-Based English). It is flexible enough to provide pattern-matching, template processing and parsing all with the same formulation, bringing these facilities to the micro-system level efficiently and economically.