Introduction

This chapter and those following describe the LKB, a lexical knowledge base system which has been designed as part of the ACQUILEX project to allow the representation of syntactic and semantic information semi-automatically extracted from machine readable dictionaries (MRDs) on a large scale. An overview of the ACQUILEX project is given by Briscoe (1991).

Although there has been previous work on building lexicons for Natural Language Processing (NLP) systems from MRDs (e.g. Carroll and Grover, 1989), most attempts at extracting semantic information have not made use of a formally defined representation language; typically a semantic network or a frame representation has been suggested, but the interpretation and functionality of the links has been left vague. Several networks based on taxonomies extracted from MRDs have been built (following Amsler, 1980) and these are useful for tasks such as sense-disambiguation, but are not directly utilisable as NLP lexicons. For a lexicon to be genuinely (re)usable, a declarative, formally specified, representation language is essential. A large lexicon has to be highly structured; it is necessary to be able to group lexical entries and to represent relationships between them, both in order to capture linguistic generalisations and to achieve consistency and conciseness. But, unless these notions of structure are properly specified, a lexicon based on them is in danger of being incomprehensible except (perhaps) to its creators.