Detecting Patterns in a Lexical Data Base

DETECTING PATTERNS IN A LEXICAL DATA BASE Nicoletta Calzolari Dipartimento di Linguistica - Universita' di Pisa Istituto di Linguistica Computazionale del CNR Via della Faggiola 32 50100 Pisa - Italy ABSTRACT In a well-structured Lexica] Data Base, a number of relations among lexica] entries can he interactively evidenced. The present article examines hyponymy, as an example of paradigmatic relation, and "restriction" relation, as a syntagmatic relation. The theoretical results of their implementation are illustrated. I INTRODUCTION In previous papers it has been pointed out that ill a well-structured Lexical Data Has(. it becomes possible to detect automatical;y, an(l ~e evidence through interactlve queries a number Of morphologica] , syntact.ic, or semant i~. relationships between lexical entries, .~uch ~lb synonymy, hyponymy, hyperonymy, der ivat ion, case-argument, lexical field, etc. The present article examines hyponymy, a.~ dI: example of paradigmatic relation, and what can b(. called "restriction or modification" relaLion, as a syntagmat ic relation, l-~y reSLl'iet Jell or modification relation, l mean that part of a so-called "aristotellan" definition which has tiJe function of linking th(~ "genus" and the "differentia specifica". When evidenced in a lexicon, tile hyponymy relation produces hierarchical trees partitioniI*K the lexicon in many semant ica i ly coilerent subsets. These trees are not created once and for al i, but it is important that uhey are procedurally activated at the query moment. While evidencing the second relation considered, one can investigate as to whether it is possible to discover any correlation be~wneI* lexical or grammatical features in definitions and particular kinds of "definienda", and thus try to answer questions such as the following: "Are there any connections between these restriction relations and ~he fundamental ways of definition, i.e. the criterial parameters by which people defines things?" For both relations, the paper presents the different procedures by which they are" automatically recognized and extracted from the natural language definitions, the degree of reliability of their automatic labeling, the use of these labels in interactive queries on the lexical data base, and finally the theoretical results of their implementation in a Machine-Dictionary. II THE LANGUAGE OF DEFINITIONS AS A SUBLANGUAGE 1 am trying to develop and exploit the idea of considering the language of dictionary definitions as a particular sublanguage within natural language. This perspective cannot obviously be adopted for subject matter restrictions in definitions, but only for the purpose of the text, i.e. the specific communicative goal. From this restriction on the purpose of the text, certain lexico-grammatical restrictions do result, which prove to be very useful. As to tile restrictions on tile lexical richness of definitions, these are not due to the fact that they relate to a specific domain of discourse, but only to the property of closure (although not satisfied at 100%') that the defining vocabulary should in principle be simpler and more restricted than the defined set of ]emmas, i.e. the former should be a proper subset of the latter. This kind of quantitative restriction on the vocabulary of definitions would not be of …

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