tailieunhanh - Báo cáo khoa học: "Chart Parsing and Rule Schemata in PSG"

MCHART is a flexible, modular chart parsing framework I have been developing (in Lisp) at Edinburgh, whose initial design characteristics were largely determined by pedagogical needs. PSG is a gr---n-tical theory developed by Gerald Gazdar at Sussex, in collaboration with others in both the US and Britain, most notably Ivan Sag, Geoff Pull,--, and Ewan Klein. It is a notationally rich context free phrase structure grumm~r, incorporating meta-rules and rule schemata to capture generalisations. (Gazdar 198Oa, 1980b, 1981; Gazdar & Sag 1980; Gazdar, Sag, Pullum & Klein to appear) In this paper I want to describe how I have. | Chart Parsing and Rule Schemata in PSG Henry Thompson Dept of Artificial Intelligence Univ of Edinburgh Hope Park Square Meadow Lane Edinburgh EH8 9NW INTRODUCTION MCHART is a flexible modular chart parsing framework I have been developing in Lisp at Edinburgh whose initial design characteristics were largely determined by pedagogical needs. PSG is a grammatical theory developed by Gerald Gazdar at Sussex in collaboration with others in both the US and Britain most notably Ivan Sag Geoff Pullum and Ewan Klein. It is a notationally rich context free phrase structure grasiaar incorporating meta-rules and rule schemata to capture generalisations. Gazdar 1980a 1980b 1981 Gazdar Sag 1980 Gazdar Sag Pullum Klein to appear In this paper I want to describe how I have used MCHART in beginning to construct a parser for grammars expressed in PSG and how aspects of the chart parsing approach in general and MCHART in particular have made it easy to accommodate two significant aspects of PSG rule schemata involving variables over categories and compound category symbols slash categories . To do this I will briefly introduce the basic ideas of chart parsing describe the salient aspects of MCHART give an overview of PSG and finally present the interesting aspects of the parser I am building for PSG using MCHaRT. Limitations of space time and will mean that all of these sections will be brief and sketchy - I hope to produce a much expanded version at a later date. I. Chart Parsing The chart parsing idea was originally conceived of by Martin Kay and subsequently developed and refined by him and Ron Kaplan Kay 1973 1977 1980 Kaplan 1972 1973a 1973b . The basic idea builds on the device known as a well formed substring table and transforms it from a passive repository of achieved results into an active parsing agent. A well formed substring table can be considered as a directed graph with each edge representing a node in the analysis of a string. Before any parsing has occurred all .