Unification Categorial Grammar: A Concise, Extendable Grammar for Natural Language Processing

Unification Categorial Grammar: A Concise, Extendable Gragamar for Natural Language Processing Jonathan CALI)F.R, Ewan KI,E1N and +Henk ZEEVAT I/niversity of Edinburgh Centre tot Cognitive Science 2 Buccleuch Place Edinbm'gh EIt8 9LW ]Institut fib' Maschinelle Sprachverarbeitung Universit,qt Stuttgm't Keplerstrasse 17 D 7000 Stuttgart Abst_~'act ~hrlication Categorial Gtmmnar (t/:G) combines the syntactic iu.,;ights of Categoria[ Grammar with the semantic insights of I)i;course Representation Theory. The addition of uni/ication to these two frameworks allows a simple account of intexaction be,.wcen different linguistic levels within a constrain- ing, monostraml theory. The resulting, computationaUy efticient, system provides an explicit formal framework for linguistic description, widfin which large fi'agments of grammms for French aud English have ah'eady been developed. We present the for- mai basis of UCG, with i.dependent definitions of well-. toxmedness fol syntactic and semantic dimensions. We will also focus on the concept of #nodifier within the theory. L lntroduetl, on Uniiieation C~tcgo~q_al Grammm' (UCG) comlfines the syntactic insights of C~tegori~ll Grammar with the semantic insights of Discourse Rep,:escntafion Theory (DRT, Kamp 1981). The addi- tion of unilicalion (Shiebcr et al. 1983) to these two flameworks allows a simple account of intcractiou between different linguistic levels. The xesulting, computationally efficient, system provkles an explicit tbmml fi'amework fbr linguistic description, within which large grammar ti'agnrents lbr French (Baschung et al. 1987) and F.nglish (Calder, Moens and Jmevat 1986) have already been developed. This paper will describe the design of the UCG formalism, illustrated by exarnples of grammatical categories and rules, l UCG embodies seve.d recent trends in linguistics. First, being a categorial grar,amar, it is strongly lexicalist, In other words rela- tively little Jr, formation is contained in grammar rules. Most information odginates in the lexicon. Second, it is strictly dechtrative. Unitication is the only operation allowed over gram- matical objects;. Third, there is a very close relationship between the syntax and semantics of linguistic expressions. UCG lies with:ht the family of grammars described by Uszkoreit 1986 and Kmttunen 1986. tJCG also has close affinities to the IIead-Driven Phrase Structure Grammar (I-IPSG) proposed by Pollard 1985. The main theoretical difference is that in IIPSG welMi~rmedrmss is characterized algorithmically, rather than declm'atively as in OC(/. For this reason, we t,ave adopted l'ollard's tenn;nology and refer to linguistic expressions as signs. A sign retm>;ents a complex of phonological, syntactic and semantic tale.nation, each of these linguistic levels having its own definitions of well--formedness, In U(.'G, we employ three primitive categories: nomts (tmun), sen- tences (sent) md noun phrases (ltp) These primitive categories i 'IIm work described here is SUl)portexl by the EEC ESPRIT projec P393 ACORD: the Cons|ruction and Interrogation of Knowledge Bases asia Natural L~mguag(~ Text and Graphics. admit further specification by features, so that we can distinguish tinite and non-finite sentences, nominative and accusative NPs, and so on. Categories are now defined as follows: (1) a. Any primitive category (together with a syntactic feature specification) is a category. b. If A is a category, and B is a sign, then A/B is a category. In …

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