TAILIEUCHUNG - Báo cáo khoa học: "PARSING CONJUNCTIONS DETERMINISTICALLY"

Conjunctions have always been a source of problems for natural language parsers. This paper shows how these problems may be circumvented using a , walt-and-see parsing strategy. A parser is presented which analyzes conjunction structures deterministically, and the specific rules it uses are described and illustrated. This parser appears to be faster for conjunctions than other parsers in the literature and some comparative timings are given. INTRODUCTION In recent years, there has been an upsurge of interest in techniques for parsing sentences containing coordinate conjunctions (and, or and but) [1,2,3,4,5,8,9]. . | PARSING CONJUNCTIONS DETERMINISTICALLY Donald w. Kosy The Robotics Institute Carnegie-Mellon University Pittsburgh Pennsylvania 15213 ABSTRACT Conjunctions have always been a source of problems for natural language parsers. This paper shows how these problems may be circumvented using a rule-based wait-and-see parsing strategy. A parser is presented which analyzes conjunction structures deterministically and the specific rules it uses are described and illustrated. This parser appears to be faster for conjunctions than other parsers in the literature and some comparative timings are given. INTRODUCTION In recent years there has been an upsurge of interest in techniques for parsing sentences containing coordinate conjunctions and or and but 1 2 3 4 5 8 9 . These techniques are intended to deal with three computational problems inherent in conjunction parsing 1. Since virtually any pair of constituents of the same syntactic type may be conjoined a grammar that explicitly enumerates all the possibilities seems needlessly cluttered with a large number of conjunction rules. 2. If a parser uses a top-down analysis strategy as is common with ATN and logic grammars it must hypothesize a structure for the second conjunct without knowledge of its actual structure. Since this structure could be any that parallels some constituent that ends at the conjunction the parser must generate and test all such possibilities in order to find the ones that match. In practice the combinatorial explosion of possibilities makes this slow. 3. It is possible for a conjunct to have gaps ellipsed elements which are not allowed in an unconjoined constituent of the same type. These gaps must be filled with elements from the other conjunct for a proper interpretation as in gave Mary a nickel and Harry a dime. The paper by Lesmo and Torasso 9 briefly reviews which techniques apply to which problems before presenting their own approach. Two papers in the list above 1 3 present deterministic .

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• PARSING CONJUNCTIONS DETERMINISTICALLY
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• Kosy
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