Incremental Interpretation of Categorial Grammar

Incremental Interpretation of Categorial Grammar* David Milward Centre for Cognitive Science University of Edinburgh 2 Buccleuch Place, Edinburgh, EH8 9LW, U.K. davidm@cogsci.ed.ac.uk Abstract The paper describes a parser for Catego- rial Grammar which provides fully word by word incremental interpretation. The parser does not require fragments of sen- tences to form constituents, and thereby avoids problems of spurious ambiguity. The paper includes a brief discussion of the relationship between basic Catego- rial Grammar and other formalisms such as HPSG, Dependency Grammar and the Lambek Calculus. It also includes a discussion of some of the issues which arise when parsing lexicalised grammars, and the possibilities for using statistical techniques for tuning to particular lan- guages. 1 Introduction There is a large body of psycholinguistic evidence which suggests that meaning can be extracted be- fore the end of a sentence, and before the end of phrasal constituents (e.g. Marslen-Wilson 1973, Tanenhaus et al. 1990). There is also recent evi- dence suggesting that, during speech processing, partial interpretations can be built extremely ra- pidly, even before words are completed (Spivey- Knowlton et al. 1994) 1. There are also potential computational applications for incremental inter- pretation, including early parse filtering using sta- tistics based on logical form plausibility, and in- terpretation of fragments of dialogues (a survey is provided by Milward and Cooper, 1994, hence- forth referred to as M&:C). In the current computational and psycholingui- stic literature there are two main approaches to the incremental construction of logical forms. One approach is to use a grammar with 'non-standard' *This research was supported by the U.K. Science and Engineering Research Council, grant RR30718. I am grateful to Patrick Sturt, Carl Vogel, and the reviewers for comments on an earlier version. 1Spivey-Knowlton et al. reported 3 experiments. One showed effects before the end of a word when there was no other appropriate word with the same initial phonology. Another showed on-line effects from adjectives and determiners during noun phrase processing. constituency, so that an initial fragment of a sen- tence, such as John likes, can be treated as a con- stituent, and hence be assigned a type and a se- mantics. This approach is exemplified by Com- binatory Categorial Grammar, CCG (Steedman 1991), which takes a basic CG with just applica- tion, and adds various new ways of combining ele- ments together 2. Incremental interpretation can then be achieved using a standard bottom-up shift reduce parser, working from left to right along the sentence. The alternative approach, exempli- fied by the work of Stabler on top-down parsing (Stabler 1991), and Pulman on left-corner parsing (Pulman 1986) is to associate a semantics directly with the partial structures formed during a top- down or left-corner parse. For example, a syntax tree missing a noun phrase, such as the following s /\ np vp John / \ v np" likes can be given a semantics as a function from enti- ties to truth values i.e. Ax. likes(john,x), with- out having to say that John likes is a constituent. …

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