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A Constraint-based Case Frame Lexicon Architecture

In Turkish, (and possibly in many other languages) verbs often convey several meanings (some totally unrelated) when they are used with subjects, objects, oblique objects, adverbial adjuncts, with certain lexical, morphological, and semantic features, and co-occurrence restrictions. In addition to the usual sense variations due to selectional restrictions on verbal arguments, in most cases, the meaning conveyed by a case frame is idiomatic and not compositional, with subtle constraints. In this paper, we present an approach to building a constraint-based case frame lexicon for use in natural language processing in Turkish, whose prototype we have implemented under the TFS system developed at Univ. of Stuttgart. A number of observations that we have made on Turkish have indicated that we need something beyond the traditional transitive and intransitive distinction, and utilize a framework where verb valence is considered as the obligatory co-existence of an arbitrary subset of possible arguments along with the obligatory exclusion of certain others, relative to a verb sense. Additional morphological lexical and semantic constraints on the syntactic constituents organized as a 5-tier constraint hierarchy, are utilized to map a given syntactic structure case-fraame to a specific verb sense.