Limits of a Sentence Based Procedural Approach for Aspect Choice in German-Russian MT

LIMITS OF A SENTENCE BASED PROCEDURAL APPROACH FOR ASPECT CHOICE IN GERMAN-RUSSIAN MT Bianka BUSCHBECK, Renat¢ HENSCHEL, Iris H6SER, Gerda KLIMONOW, Andreas K(ISTNER, Ingrid STARKE Zentralinstitut ffir Sprachwissenscha~, Berlin Prenzlauer Promenade 149-152 O-1100 Berlin ABSTRACT In this paper we discuss some problems arising in German-Russian Machine Translation with regard to tense and aspect. Since the formal category of aspect is missing in German the information required for generating Rus- sian aspect forms has to be extracted from different representation levels. A sentence based procedure for aspect choice in the MT system VIRTEX is presented which takes lexieal, morphological and semantic criteria into account. The limits of this approach are shown. To overcome these difficulties a human interaction compo- nent is proposed. INTRODUCTION Aspect is considered to bca grammatico-semanticai category for expressing various temporal references in relation to the speech act moment. Regardless of the great number of special meanings that can be expressed by the perfective or imperfectiv¢ aspect (p.asp./i.asp.), there are two oppositions representing the systematic or basic aspectual meanings, namely +TOTALITY/+LIM/TEDNESS VerSus -TOTAL1TY/-LIMITEDNESS (see Bondarko 1990). In this paper we will discuss the transfer of tense and aspect, a problem which arises immediately in Machine Translation and differS from language pair to language pair. This mainly depends on how aspect is expressed in the particular languages concerned. It is obvious that aspect in several languages has a rather heterogeneous formal reflection in the verb system. Aspect and tense are closely connected with each other. In English, e.g., the two aspect constructions perfective and progressive can be seen as realizing the basic contrast of the action viewed as complete or as incomplete (for details see van Eynde 1988). All Slavic languages on the other hand have a well- formed aspect system where verbs have a perfective and an imperfectivc aspect derived from the verbal stem by affixation. The translation of verbal groups from English into Russian, for example, seems to be possible by for- mulating rules which assign concrete Russian aspect forms to several combinations of tense and aspect in English, e.g. has been giving (present perfect continuous) -> zr~Ba/r (past, imperfective aspect) has given (present perfect) --> ~ra~ (past, perfective aspect) (ef. Apresjan 1989: 154). In contrast to the languages mentioned above, aspect meaning in German, which doubtlessly exists, has no explicit formal expression. Therefore, aspect information required for translation into Russian has to be extracted from different levels of text representation. This is necessary since without the correct choice of Russian aspect serious translation errors in the target language could occur. In our German-Russian MT project VIRTEX we have approached this problem by constructing a hierarchic procedure for aspect choice (presented in the next paragraphy which takes a complex of contextual, morphological and semantical criteria into account. If the aspect choice algorithm fails to select one of the two aspect forms, wider context (beyond the bound-aries of sentence) or background knowledge must be taken into consideration. To meet this difficulty VIRTEX is provided with a system of …

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