Lexical choice as pattern matching

Abstract

A good lexical component is a vital part of any natural-language system. The paper discusses an implemented lexical component that is part of a larger system currently being developed for information retrieval. Two special features of the system are its unique knowledge-representation formalism on the various levels, conceptual graphs, and a unique lexicon for the parser and the generator. Lexical choices depend on various knowledge sources (pragmatic, conceptual, linguistic etc). The conceptual component, i.e. the words' underlying meanings or definitions, are discussed in the paper. The authors believe that word meanings and utterance meanings are isomorphic, in the sense that (a) words, sentences and texts are simply different units for conveying a message (words being shorthand labels for larger conceptual chunks), and (b) the core meanings of words and texts (sentences) can be expressed by the same formalism: conceptual graphs. This view allows the process of lexical choice to be modelled by matching definition graphs (word definitions) on an utterance graph (conceptual input). Further, it provides a natural basis for paraphrases and for explanations concerning the conceptual differences between a set of words.