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Conjunctions are particularly difficult to parse in traditional, phra.se-based gramniars. This paper shows how a different representation, not b.xsed on tree structures, markedly improves the parsing problem for conjunctions. It modifies the union of phra.se marker model proposed by GoodalI [19811, where conjllnction is considered as tile linearization of a three-dimensional union of a non-tree I),'med phrase marker representation. | New Approaches to Parsing Conjunctions Using Prolog Sandiway Fong Robert c. Berwick Artificial Intelligence Laboratory M.I.T. 545 Technology Square Cambridge MA 02139 U.S.A. Abstract Conjunctions are particularly difficult to parse in traditional phrase-based grammars. This paper shows how a different representation not based on tree structures markedly improves the parsing problem for conjunctions. It modifies the union of phrase marker model proposed by Goodall 1981 where conjunction is considered as the linearization of a three-dimensional union of a non-tree based phrase marker representation. A PROLOG grammar for conjunctions using this new approach is given. It is far simpler and more transparent than a recent phrase-based extraposition parser conjunctions by Dahl and McCord l934 . Unlike the Dahl and McCord or ATN SYSCONJ approach no special trail machinery is needed for conjunction beyond that required for analyzing simple sentences. While of comparable efficiency the new approach unifies under a single analysis a host of related constructions respectively sentences right node raising or gapping. Another advantage is that it is also completely reversible without cuts and therefore can be used to generate sentences. Introduction The problem addressed in this paper is to construct a grmnmatical device for handling coordination in natural language that is well founded in linguistic theory and yet computationally attractive. The linguistic theory should be powerful enough to describe all of the phenomenon in coordination but also constrained enough to reject all ungrammatical examples without undue complications. It is difficult to achieve such a line balance - especially since the term grammatical itself is highly subjective. Some examples of the kinds of phenomenon that must be handled are shown in fig. I The theory should also be amenable to computer implementation. For example the representation of the phrase marker should be conducive to both dean process
