The ACQUILEX LKB: representation issues in semi-automatic acquisition of large lexicons

The ACQUILEX LKB: representation issues in semi-automatic acquisition of large lexicons Ann Copestake University of Cambridge Computer Laboratory New Museums Site, Pembroke Street, Cambridge, CB2 3QG, UK Ann.Copestake@cl.cam.ac.uk Abstract We describe the lexical knowledge base sys- tem (LKB) which has been designed and im- plemented as part of the ACQUILEX project 1 to allow the representation of multilinguM syn- tactic and semantic information extracted from machine readable dictionaries (MRDs), in such a way that it is usable by natural language processing (NLP) systems. The LKB's lex- ical representation language (LRL) augments typed graph-based unification with default in- heritance, formalised in terms of default unifi- cation of feature structures. We evaluate how well the LRL meets the practical requirements arising from the semi-automatic construction of a large scale, multilingual lexicon. The system as described is fully implemented and is being used to represent substantial amounts of infor- mation automatically extracted from MRDs. 1 Introduction The ACQUILEX LKB is designed to support repre- sentation of multilingual lexical information extracted from machine readable dictionaries (MRDs) in such a way that it can be utilised by NLP systems. In con- trast to lexical database systems (LDBs) or thesaurus- like representations (e.g. Alshawi et al., 1989; Calzolari, 1988) which represent extracted data in such a way as to support browsing and querying, our goal is to build a knowledge base which can be used as a highly struc- tured reusable lexicon, albeit one much richer in lexi- cal semantic information than those commonly used in NLP. Thus, although we are using information which has been derived from MRDs (possibly after consider- able processing involving some human intervention), our aim is not to represent the dictionary entries themselves. Our methodology is to store the dictionary entries and raw extracted data in our LDB (Carroll, 1990) and to use this information to build LKB entries which could be directly utilised by an NLP system. Briscoe (1991) discusses the LDB/LKB distinction in more detail and describes the ACQUILEX project as a whole. 1'The Acquisition of lexical knowledge for Natural Lan- guage Processing systems' (Esprit BRA-3030) Practical NLP systems need large lexicons. Even in cases such as database front ends, where the domain of the application is highly restricted, a practical natural language interface must be able to cope with an exten- sive vocabulary, in order to respond helpfully to a user who lacks domain knowledge, for example. For applica- tions such as text-to-speech synthesis, interfaces to large- scale knowledge based systems, summarising and so on, large lexicons are clearly needed; for machine transla- tion the requirement is for a large scale, multilingua] lexical resource. Acquisition of such information is a serious bottleneck in building NLP systems, and MRD sources currently seem the most promising source for semi-automatically acquiring the syntactic and semantic information needed. Previous work on extracting and representing syntac- tic information includes the work done on the Alvey Tools lexicon project (Carroll and Grover 1989) in which a large scale lexicon was produced semi-automatically from LDOCE …

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