Parsing with Categorial Grammar in Predictive Normal Form

Abstract

Steedman (1985, 1987), Dowty (1987), Moortgat (1988), Morrill (1988), and others have proposed that Categorial Grammar, a theory of syntax in which grammatical categories are viewed as functional types, be generalized in order to analyze “noncanonical” natural language constructions such as whextraction and nonconstituent conjunction. A consequence of these augmentations is an explosion of semantically equivalent derivations admitted by the grammar, a problem we have characterized as spurious ambiguity from the parsing perspective (Wittenburg, 1986). In Wittenburg (1987), it was suggested that the offending rules of these grammars could take an alternate predictive form that would eliminate the problem of spurious ambiguity. This approach, consisting of compiling grammars into forms more suitable for parsing, is within the tradition of discovering normal forms for phrase structure grammars, and thus our title. Our approach stands in contrast to those which are attempting to address the spurious ambiguity problem in Categorial Grammars through the parsing algorithm itself rather than through the grammar (see Gardent & Bes, 1989; Pareschi & Steedman, 1987) and also to those addressing the problem by proof-theoretic means in the Lambek calculus tradition (Bouma, 1989; Hepple & Morrill, 1989; Koenig, 1989; Lambek, 1958; Moortgat, 1986, 1988). We follow the line of Steedman (1985, 1987), Dowty (1987), and various strains of Categorial Unification Grammar (Karttunen, 1986; Uszkoreit, 1986; Wittenburg, 1986; Zeevat, Klein & Calder, 1987) in that we assume a finite number of combinatory rules and study the behavior of parsers that apply these rewrite rules in roughly the phrase-structure parsing tradition.