Structural Non-Correspondence in Translation

STRUCTURAL NON-CORRESPONDENCE IN TRANSLATION Louisa Sadler, Dept. of Language and Linguistics, University of Essex, Wivenhoe Park, Colchester, CO4 3SO, Essex, UK. loulsa@uk.ac.essex Henry S. Thompson, Human Communication Research Centre, University of Edinburgh, 2 Buccleuch Place, Edinburgh, EH8 9LW, UIC ht@uk.ac.ed.cogsci ABSTRACT Kaplan et al (1989) present an approach to machine translation based on co-description. In this paper we show that the notation is not as natural and expressive as it appears. We first show that the most natural analysis proposed in Kaplan et al (1989) cannot in fact cover the range of data for the important translational phenomenon in question. This contribution extends the work reported on in Sadler et al (1989) and Sadler et al (1990). We then go on to discuss alternatives which depart from or extend the formalism proposed in Kaplan et al (1989) in various respects, pointing out some directions for further research. The strategies discussed have been implemented. 0. Introduction Recent work in LFG uses the notion of projection to refer to linguistically relevant map- pings or convspondences between levels, whether these mappings are direct or involve function composition (I-lalvorsen & Kaplan (1988), Kaplan (1987), Kaplan et al (1989)). Mapping functions such as V (from c to f struc- ture) and o (from c to semantic structure) are familiar from the LFO literhture. Kaplan et al (1989) extend this approach to Machine Transla- tion by defining two translation functions "~ (between f-structures) and "~' (between semantic structures). By means of these functions, one can 'co-describe' elements of source and target f-structures and s-structures respectively. Achieving translation can be thought of in terms of specifying and resolving a set of constraints on target structures, constraints which are expressed by means of the "~ and "c' functions. The formalism permits a wide variety of sourco-target correspondences to be expressed: T and V can be composed, as can -c' and o. The approach allows for equations specifying trans- lations to be added to lexical entries and (source language) c-structure rules. For example: (1) (~ (? SUB.0) = ((~ 1) SUBJ) composes "~ and ap, equating the ~ of the SUBJ f-structure with the SUBJ attribute of the "c of the mother's f-structure. Thus (1) says that the translation of the value of the SUBJ slot in a source f-structure fills the SUBJ slot in the f- structure which is the translation of that source f-structure. What results is an interesting, and apparently extremely attractive approach to MT, which finds echoes in a good deal of recent work in MT and Computational Linguistics gen- erally (van Noord et al (1990), Zajac (1990)). Among the apparent advantages are: (i) that it avoids the problems that arise in traditional stratificational transfer systems where a variety of (often incompatible) kinds of information must be expressed in a single structure. (ii) that, because it uses the formal apparatus of LFG, it is at least compatible with a large body of well worked out linguistic analyses. Perhaps most important, however, the examples that Kaplan …

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