Study of Efficient Parsing Methods Based on Japanese Phrase Structure Grammar

在这项研究中，我们试图开发一个适合计算机处理自然语言的语法描述系统。我们的重点是语法理论中固有的机制，特别是如何描述约束。为了实现这一目标，我们开发了一种有效的语法描述形式化方法来实现语法理论。在此基础上，我们开发了一个句法分析系统的原型，并在此基础上实现了日语短语结构语法的核心部分。1991年和1992年，我们的重点是描述与语法概括相关的约束的通用方法。我们还注意了在计算环境中实现语言要求的语法约束的自然和有效的方法。1992年，我们开发了语法分析机制和语法描述形式，作为独立的模块，并试图使交叉引用过程明确。1992和1993年，我们首先将现有的自上而下的分析算法转换为自下而上的程序，并开发了一些工具来最小化语法描述与其实现之间的差异。结果，我们发现，我们提出的句子结构的多层特征表示不仅可以统一处理形态表示和语义表示，而且可以开发基于这种表示的句法分析系统。尽管我们首次尝试将连续代价的概念引入到我们的约束库存中，但是在逻辑规划的离散系统中引入这种连续概念的方法并没有得到令人满意的结果。我们希望在不久的将来在一个单独的研究项目中处理这个问题。

In this study, we have attempted to develop a gramr description system suited for computer processing of natural language. Our focus was on mechanisms inherent in grammatical theory, in particular, on how constraints are described. In order to achieve this goal, we have developed an efficient gramr description formalism with which to implement grammatical theory. With this formalism, we have developed a prototype of a parsing system and implemented the core part of Japanese Phrase Structure Grammar on it.In 1991 and 1992, our focus was on the genaral method of describing constraints associated with grammatical generalizations. We also paid attention to natural and efficient ways for implementing linguistically-required grammatical constraints in a computational environment. In 1992, follwing these results, we have developed a parsing mechanism and a grammatical description formalism employed by the parser as separate modules and tried to make the crossreferencing procedure explicit.In 1992 and 1993, we first transformed the existing top-down parsing algorithm into a bottomup program and developed some tools for minimizing the discrepance between grammatical description and its implementation.As the result, we have found out that multi-layred feature representation for sentence structures we have proposed in this research not only make it possible to uniformly treat morphological representation and semantic representation but also make it feasible to develop a parsing system based on such representation.Even though we have first attempted to introduce the concept of continuous cost into our inventory of constraints, we have not arrived at a satisfactory result on the way of introducing such continuous concept in the discrete system of logic programming. We hope to handle this problem in a separate research project in the near future.