The need for MT-oriented versions of Case and Valency in MT

The need for MT-oriented versions of Case and Valency in MT Harold L. Somers Centre for Computational Linguistics University of Manchester Institute of Science & Technology ABSTRACT This paper looks at the use in machine Translation systems of the linguistic models of Case and Valency. It is argued that neither of these models was originally developed with this use in mind, and both must be adapted somewhat to meet this purpose. In particular, the traditional Valency distinction of complements and adjuncts leads to conflicts when valency frames in different languages are compared: a finer but more flexible distinction is required. Also, these concepts must be extended beyond the verb, to include the noun and adjective as valency bearers. As far as Case is concerned, too narrow an approach has traditionally been taken: work in this field has been too conerned only with cases for arguments in verb frames; case label systems for non- valency bound elements and also for elements Jn nominal groups must be elaborated. The paper suggests an integrated approach specifically oriented towards the particular problems found in MT. ]. Introduction Most (though not all) MT systems claim to incorporate versions of Valency grammar, and more recently have also looked to Case grammar. However, whatever theory they use is often imported more or less directly, without taking account of the fact that a model developed for one purpose may not be entirely appropriate for another. This is a less serious problem for Valency, though this was originally designed with a monolingual didactic purpose in mind (see Helbig & Schenkel, 1973:5) rather than the multiling~al needs of translation. With Case however, it is often the much-maligned and quickly supereeded Fillmore (1968) model which is adopted, or at best a 'consensus' model like that of Fillmore (1971) or Chafe (1970), loosely extended. What is not taken into account is the fact that these models typically concentrate on 'nuclear' arguments in verb- phrases, saying little about 'peripheral' roles, or about the structure of nominal or even adjectival groups. This paper will show need for a more task- specific model, combining Valency and Case into an integrated theory for the purposes of translation. More specifically, we will show (a) the need for a more flexible Valency system with six degrees of valency-binding instead of the usual two; (b) the need for a finely tuned version of Case to fit the new version of Valency proposed: in particular what depth of abstraction is appropriate; and (c) the need for this combined Case and Valency model to extend beyond verbs, especially to nominal groups. 2. Valency in existing MT systems The essential notion borrowed from Valency theory found in MT is the distinction between 'complements' and 'adjuncts'. In several MT systems we find that the lexicon contains information equivalent to that given in a valency dictionary like that of Helbig & Schenkel (1973) listing the complements predicted by the verb together with associated syntactic and semantic features. This lexical information is used in a …

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