Parsing with Discontinuous Constituents

Parsing with Discontinuous Constituents Mark Johnson Center for the Study of Language and Information and Department of LinKuktics, StLnford University. Abstract By generalizing the notion of location of a constituent to allow discontinuous Ioctaions, one can describe the discontinuous consti- tuents of non-configurational languages. These discontinuous consti- tuents can be described by a variant of definite clause grammars, and these grammars can be used in conjunction with a proof pro- cedure to create a parser for non-configurational languages. 1. Introduction In this paper [ discuss the problem of describing and computa- tionally processing the discontinuous constituents of non- configurational languages. In these languages the grammatical func- tion that an argument plays in the clause or the sentence is not determined by its position or confguration in the sentence, as it is in configurational languages like English, but rather by some kind of morphological marking on tile argument or on the verb. Word order in non-configurational languages is often extremely free: it has been claimed that if some string of words S is grammatical in one of these languages, then the string S' formed by any arbitrary permutation of the words in S is also grammatical. Most attempts to describe this word order freedom take mechanisms designed to handle fairly rigid word order systems and modify them in order to account for the greater word order freedom of non-configurational languages. .Mthough it is doubtful whether any natural language ever exhibits such total scrambling, it is interesting to investigate the computa- tional and linguistic implications of systems that allow a ifigh degree of word order freedom. So the approach here is the opposite to the usual one: I start with a system which, unconstrained, allows for unrestricted permutation of the words of a sentence, and capture any word order regularities the language may have by adding res- trictions to the system. The extremely free word order of non- configurational languages is described by allowing constituents to have discontinuous [ocatio,ls. To demonstrate that it is possible to parse with such discontinuous constituents. I show how they can be incorporated into a variant of definite clause grammars, and that these grammars can be used in conjunction with a proof procedure. such as Ear[ey deduction, to coestruct a parser, a.s shown in Pereira and Warren (1983). This paper is organized as follows: section 2 contains an infor- mal introduction to Definite Clause Grammars and ,lisctmses how they can be used in parsing, section :l giws a brief description of some of the grammatical features of o**o non-,'onligurational language. Guugu Yimhlhirr, section I presents ;t deiinite clause frag- ment for this language, aml shows how this can be u~ed for parsing. Section 5 notes that the use of di~conti*uiot*s con.~l.ituent.~ is *lot lim- ited to definite clause granunars. [)lit they could lie incorporated into such disparate formalisnts as GP~(;, I,FG or (';[L Section 6 discusses whether a unified account of par.qng both conligurational and non-configurational languages can be given, and section 7 com- pares the notion …

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