From Submit to Submitted via Submission: On Lexical Rules in Large-Scale Lexicon Acquisition

This paper deals with the discovery, representation, and use of lexical rules (LRs) during large-scale semi-automatic computational lexicon acquisition. The analysis is based on a set of LRs implemented and tested on the basis of Spanish and English businessand finance-related corpora. We show that, though the use of LRs is justified, they do not come costfree. Semi-automatic output checking is required, even with blocking and preemtion procedures built in. Nevertheless, largescope LRs are justified because they facilitate the unavoidable process of large-scale semi-automatic lexical acquisition. We also argue that the place of LRs in the computational process is a complex issue. 1 I n t r o d u c t i o n This paper deals with the discovery, representation, and use of lexical rules (LRs) in the process of largescale semi-automatic computational lexicon acquisition. LRs are viewed as a means to minimize the need for costly lexicographic heuristics, to reduce the number of lexicon entry types, and generally to make the acquisition process faster and cheaper. The findings reported here have been implemented and tested on the basis of Spanish and English businessand finance-related corpora. The central idea of our approach that there are systematic paradigmatic meaning relations between lexical items, such that, given an entry for one such item, other entries can be derived automa t i ca l l y is certainly not novel. In modern times, it has been reintroduced into linguistic discourse by the Meaning-Text group in their work on lexical functions (see, for instance, (Mel'~uk, 1979). § also of US Department of Defense, Attn R525, Fort Meade, MD 20755, USA and Carnegie Mellon University, Pittsburgh, PA. USA. §§ also of Purdue University NLP Lab, W Lafayette, IN 47907, USA. It has been lately incorporated into computational lexicography in (Atkins, 1991), (Ostler and Atkins, 1992), (Briscoe and Copestake, 1991), (Copestake and Briscoe, 1992), (Briscoe et al., 1993)). Pustejovsky (Pustejovsky, 1991, 1995) has coined an attractive term to capture these phenomena: one of the declared objectives of his 'generative lexicon' is a departure from sense enumeration to sense derivation with the help of lexical rules. The generative lexicon provides a useful framework for potentially infinite sense modulation in specific contexts (cf. (Leech, 1981), (Cruse, 1986)), due to type coercion (e.g., (eustejovsky, 1993)) and similar phenomena. Most LRs in the generative lexicon approach, however, have been proposed for small classes of words and explain such grammatical and semantic shifts as +coun t to c o u n t or c o m m o n to + c o m m o n . While shifts and modulations are important , we find that the main significance of LRs is their promise to aid the task of m ass i ve lexical acquisition. Section 2 below outlines the nature of LRs in our approach and their status in the computational process. Section 3 presents a fully implemented case study, the morpho-semantic LRs. Section 4 briefly reviews the cost factors associated with LRs; the argument in it is based on another case study, the adjective-related LRs, which is especialy instructive since it may mislead one into thinking thai. LRs are unconditionally beneficial. 2 N a t u r e o f L e x i c a l R u l e s 2.1 O n t o l o g i c a l S e m a n t i c B a c k g r o u n d Our approach to NLP can be characterized as ontology-driven semantics (see, e.g., (Nirenburg and Levin, 1992)). The lexicon for which our LRs are introduced is intended to support the computational specification and use of text meaning representations. The lexical entries are quite complex, as they must contain many different types of lexical knowledge that may be used by specialist processes for automatic text analysis or generation (see, e.g.,