A Tool for Investigating the Synonymy Relation in a Sense Disambiguated Thesaurus

A TOO1. FOR INVESTIGATING TIlE SYNONYMY RELATION IN A SENSE DISAMBIGUATED THESAURUS Martin S. Chodorow IBM T.J. Watson Research Center Yorktown Heights, New York 10598 and Department of Psychology, Hunter College of CUNY New York, New York 10021 Yael Ravin IBM T.J. Watson Research Center Yorktown Heights, New York 10598 ltoward E. Sachar IBM Data Systems Division White Plains, New York 10601 Abstract This paper describes an exploration of the implicit synonymy relationship expressed by synonym lists in an on-line thesaurus. A series of automatic steps was taken to properly con- strain this relationship. The resulting groupings of semantically related word senses are believed to constitute a useful tool for natural language processing and for work in lexicography. Introduction The importance of semantic processing of natural language i:, generally acknowledged (Grishman 1986) and needs no justification. Work on applications such as information re- trieval or machine translation has consistently focused on semantic analysis. A wide range of models has been suggested, based on semantic networks, on fuzzy logic, on conceptual de- pendencies and more. Common to all these models, however, is the researchers' reliance on hand-built semantic databases. These da- tabases tend to be rather limited in scope and often restricted to narrow domains. If the process of constructing them remains manual, broad-coverage semantic analysis by comput- ers will be severely handicapped for quite a long time. It is our goal, therefore, to explore automatic and semi-automatic ways of con- structing these semantic databases, through the manipulation of machine-readable semantic sources. In this paper, we concentrate on heuristics for the automatic manipulation of synonyms found in an on-line thesaurus. First, we should clarify what we mean by "synonyms". The definition of synonymy and the existence of synonyms have long been de- bated in linguistics. Some believe it is impos- sible to capture meaning, not even of the most concrete terms in natural language. Conse- quently, it is impossible to define synonymy or to identify synonymous terms (Quine 1960). Others believe it is possible to give full seman- tic representations of meaning and therefore to define synonymy formally and to identify true synonyms (Katz and Fodor 1963). According to this view, synonymy is a relationship of sameness of meaning between words, which is defined as the identity of their semantic rep- resentations. We have chosen an operational approach to synonymy: The synonyms of a headword w are whatever words are listed in the entry for w in an on-line version of The New Collins Thesaurus (1984) (C'I'). l According to the au- thors, "...no synonym is entered unless it is fully substitutable for the headword in a sensi- We have stored CT as a DAM file (Byrd, et al., 1986) with 16,794 keyed records containing a total of 287,136 syn- onym tokens. It has been supplemented with part-of-speech information from the UDICT computerized lexicon system (Byrd, 1986). 144 ble English sentence" (Collins 1984:v). This may suggest that each entry (i.e., a headword and its synonym list) contains all and only words …

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