Processing Word Order Variation Within a Modified ID/LP Framework

PROCESSING WORD ORDER VARIATION WITHIN A MODIFIED ID/LP FRAMEWORK Pradip Dey University of Alabama at Birmingham Birmingham~ AL 35294~ U.S.A. ABSTRACT From a well represented sample of world languages Steele (1978) shows that about 70% of languages exhibit significant word order variation. Only recently has this wlde-spread phenomenon been drawing appropriate attention. Perhaps ID/LP (Immediate Dominance and Linear Precedence) framework is the most debated theories in this area. We point out some difficulties in processing standard ID/LP grammar and present a modified version of the grammar. In the modified version, the right hand side of phrase structure rules is treated as a set or partially ordered set. An instance of the framework is implemented. 1. Introduction From a well represented sample of world languages Steele (1978) ~,~hows that about 76~ of the languages exhibit significant word order variation | . Until recently thls widespread phenomenon was not given proper attention in natural language processing. The primary goal of tbis study is to develop eomputatlonally efficient and linguistically adequate strategles for parsing word order variation. The strategies are implemented in a network based parser. At first we characterize the basic problem at an abstract level without going into details of the problem in any specific language (in Section-2). Then~ in Sectlon-3, the details of the problems in a specific language~ namely~ Iilndi~ are presented. The Immediate dominance and linear precedence (ID/LP) framework~ developed by Gazdar and Pullum~ is one of the most debated theories in the study of word order variation (Pullum 1982~ Uszkorelt 1082, Shieber 1983, Barton 1985). The basic idea behind ID/LP framework is to separate immediate dominance from linear precedence in rewrite rules. Pullum (1982) expresses this via a metagrammar. The modified version presented in this paper expresses this directly in the object grammar eliminating the need for a metagrammar. It treats the right hand side of a PS (Phrase Structure) rule as a set or partially ordered set. Parsing with this type of rule can proceed by checking set membership. 2. The Word Order Problem in General The word order problem is the problem of processing the whole range of word order variation occurring in natural languages. Some Australian languages such as Warlpiri show extreme word order variation (Hale 1983). Hindi, Japanese and German also allow considerable word order variation. In this section we develop descriptive formalisms and parsing mechanisms that are adequate for the whole range of word order variation. Consider a grammar thdt allows a node labeled S to have daughters labeled $, O, and ¥ in any linear order~ and nothing else. Such a grammar can be presented with a set of rules such as that given in (2.1). (2.1) S --> $ OV, S --> $VO, S --> 0 SV, S--> OV$, S--> V$O, S--> VO$ The problem with a grammar such as that given in (2.1) is that i~ needs too many rules to capture word order variation (in this case free word order). For 5 'words' such a grammar will need …

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