STS: An Experimental Sentence Translation System

STS: An Experimental Sentence Translation System Eric Wehrli* University of Geneva 1211 Geneva 4 wehrli@uni2a.unige.ch Abstract STS is a small experimental sentence translation system developed to demonstrate the efficiency of our lexicalist model of translation. Based on a GB-inspired parser, lexical transfer and lexi- cal projection, STS provides real-time accurate English translations for a small but non-trivial subset of French sentences. 1 Introduction As a preliminary step towards the develop- ment of an on-line interactive system, we de- velop the STS system to establish whether our lexicalist translation model, using a GB-.inspired parser, lexical transfer and lexical projection, provides the kind of efficiency required for on- line translation 2. In its present implementa- tion, STS translates sentences from French to English. It can handle a limited, although not trivial subset of clausal structures, using a lexi- cal database of more than 5,000 entries (includ- ing compounds and idiomatic expressions). Accurate natural language translation requires a wide range of cognitive abilities, including gram- matical knowledge of the languages involved but also some amount of extralinguistic knowledge and common sense reasoning. Lack of weU- defined theoretical models of knowledge and conmlon sense reasoning makes fully automatic high quality translation unlikely in the near fu- ture. In the meantime, what appears to be an in- creasingly appealing alternative is on-line inter- active machine translation, i.e. systems which can consult the user when they are unable to solve a problem 1. However, in order to be a viable alternative to other machine or machine- aided translation models, and in addition to the usual requirements of reasonable quality and low cost, an on-line interactive system must also sat- isfy the requirements of real-time systems and in particular be fast enough not to use the user's patience. *Part of the work described in this paper has been supported by a grant from the Swiss national science foundation (grant no 11-25362.88). 'For a discussion of on-line interactive translation see Kay (1982), Tomita (1986), Johnson and Whitelock (1987), among others. 2 Architecture of the system The basic architecture of the STS system is the familiar transfer model with its three main com- ponents: analysis, transfer and generation. To see how these components interact, consider the following (drastically oversimplified) sketch of the translation process: an input sentence in the source language (SL) is first mapped onto some formal representation for this language (S- structure). This is done by the parser, on the basis of lexical information and detailed knowl- edge about the grammar of SL. The transfer component maps then the S-structure :returned by the parser onto an appropriate S-structure in the target language. The transfer is done con- stituent by constituent, in a top-down fashion, starting with the top S (or S) constituent. For each constituent, the lexical head is first con- sidered: Its lexeme is associated with a set of possible translations, ie. one or more lexemes in the target language. Once the relevant lex- eme has been selected an appropriate structure is projected on the basis …

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