          NIVES MIKELIĆ PRERADOVIĆ, DAMIR BORAS; TOMISLAVA LAUC Department of Information and Communication Sciences Faculty of Humanities and Social Sciences, University of Zagreb I. Lucica 3, 10000 Zagreb CROATIA nmikelic@ffzg.hr , dboras@ffzg.hr , tlauc@ffzg.hr Abstract:  In this paper we aim to describe the latest work on the syntactic5semantic classification of verbs in Croatian language. We tried to extract the specific semantics and function of verb prefixes in Croatian and capture these specific features in the Croatian verb valency lexicon CROVALLEX. The syntactic and semantic connection between base verbs and derived prefixed verbs is revealed and modelled as rules which contribute to the enrichment of the CROVALLEX lexicon. KeyWords:  verbal prefixes, Croatian Verb Valency Lexicon, verb semantics, syntacto5semantic verb classification, derivational rules, Aktionsart   The goal of this paper is to present and evaluate the improvement of syntactic5semantic verb classification in Croatian Valency Lexicon (CROVALLEX). CROVALLEX [5] is the first Croatian verb lexicon that contains valency frames of Croatian verbs crucial for many Natural Language Processing (NLP) tasks, such as parsing, tagging, machine translation, syntactic analysis or word sense disambiguation (WSD) of Croatian language. It contains 1739 verbs associated with 5118 valency frames (which makes an average of 3 valency frames per verb). Those 1739 verbs were selected from the Croatian frequency dictionary [12] according to their number of occurrences. The background theory in CROVALLEX is valency theory, developed by Czech linguists Petr Sgall and his collaborators as the part of the Functional Generative Description [6], used for the description of valency frames in CROVALLEX. The valency frame in CROVALLEX consists of the set of syntactic arguments that the specific verb demands or grammatically allows. The type of valency relation for each argument is marked up as obligatory “obl” or typical optional “typ”. Since most of the verbs in Croatian are polysemic, each verb meaning requires unique morphemic form for all its obligatory and optional arguments. That morphemic form is stored in CROVALLEX together with the information about their obligatoriness or optionality. CROVALLEX distinguishes obligatory complements / thematic roles (e.g. Agent5AGT, Patient5PAT, Recipient5 REC, Result5RESL, etc.) and typical optional complements (LOC5location, CAUS5cause, HER5 heritage, etc).    !" The most productive type of verb derivation in Croatian is prefixation, a derivational process that attaches the prefix to a verbal stem resulting in a new lexical item. The verbal aspect of Croatian verbs is always marked, i.e. the verb infinitive can have either perfective or imperfective form. The prefixation of an imperfective verb can either yield an imperfective verb (davati/to give– davati/to add) or a perfective verb (kuhati/to cook – kuhati/to finish cooking). On the other hand, the prefixation of a perfective verb can yield only perfective forms (baciti/to throw – baciti/to throw out), since imperfective forms of a perfective verb are built through suffixation (baciti/to throw – bac++ti/to throw over and over again). Although being described in general grammars and dictionaries of Croatian language [2, 3], the current state of knowledge regarding different properties of verb prefixation is inconclusive. On the other hand, the close relationship between the verbal aspect and Aktionsart (defined as a syntactic5semantic category covering the manner of action, action type, verbal character or aspectual Recent Advances in Computer Science ISBN: 978-960-474-311-7 35