A Parametric NL Translator

A Parametric NL Translator Randall Sharp Dept. of Computer Science University of British Columbia Vancouver, Canada Abstract This report outlines a machine translation system whose linguistic component is based on principles of Government and Binding. A "universal grammar" is defined, together with pal-ameters of variation for specific languages. The system, written in Prolog, parses, generates, and translates between English and Spanish (both directions). i. Introduction The theory of Gov~t and Binding (GB) (Chc~sky 1981) proposes universal principles of grammar (UG) that underlie all natural grammars, with the principles being subject to parametrization, giving rise to language variation. One example is the so- called "pro-drop" parameter of languages like Spanish, Hungarian, C~ineae, etc., that, among other things, allow '%dssing" subjects. To model such a theory, one needs merely (~) to define the UG along with an appropriate set of parameter values for each language, as opposed to defining totally independent language-specific grammars. The overall size of the system is thereby reduced, and adding the grammar for a new language ideally means simply adding its parameter settings. Hence the motivation for a GB approach to machine translation. To test the approach, a model of UG was constructed, parameters defined for Spanish and English, and language-specific rules added for morphology and, where necessary, idiosyncratic syntax. The result is the GB-Translator (GBT) (Sharp 1985). A general knowledge of GB is assumed in the following, as is a familiarity with Prolog, the language in which the GBT is implemented. The overall strategy of the GBT is as follows: (I) a. read in a sentence in the source language; b. perform a morphological and constituent analysis, building an S-structure representation; c. convert the S-structure to D- ("deep") structure via reverse-transformations; d. perfor~ lexical transfer frc~ the source D- structure to target D-structure; e. transform the D-structure to one or more S- structures; f. validate each S-structure for well-formed- hess; g. "flatten" and display only the well-form~l target sentences. Since GB is primarily a theory of syntax, no seman- tic processing has been introduced in the GBT. What is of interest here is the variety of syntactic forms available in diverse languages for expressing semantically equivalent propositions, with "equi- valence,, being controlled by appropriate choices of lexical items in the two languages. Problems of semantic ambiguity and structural alteration have not been addressed, as this relates more to trans- lation theory than to GB. An example of the system's behavior is shown below, where user responses are underlined: (2) Enter source language: 9_e_e~lish. Enter target language: ~ish. Enter sentence in english: I believe John to have told the truth. Yo creo clue Juan ha dicho la verdad. Creo que Juan ha dicho la verdad. Enter source language: ~L3anish. Enter target language: ~lish. Enter sentence in spanish: Creo que has dicho la verdad. I believe that you have told the truth. I believe you have told the truth. I believe you to have told the truth° 2. System Structure The GBT contains a UG conioonent and two language- …

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