Generating French with a Reversible Unification Grammar

O. Intr~cluction In this paper, we describe the linguistic solutions to some of the problems encountered in writing a reversible French grammar. This grammar is primarily intended to be one of the components of a machine translation system built using ELU, 1 an enhanced PATR-II style unification grammar linguistic environment based on the LID system described in Johnson and Rosner (1989), but it is also part of our more general experimentation with fully reversible grammars. The requirement that it be reversible imposes a stringent criterion of linguistic adequacy on a grammar, siuce it is not allowed to overgenerate while it must at the same time provide a large coverage for analysis (Dymetman and IsabeUe (1988)). Formally, grammars that are fully reversible must be completely declarative, since no reierence can be made in the grammar rules to the process (analyzer or synthesizer) which will use them. The unification formalism makes itt possible to write such grammar statements, because due to the associativity and commutativity of the unitication operation, the result of unifying feature structures is independent of the order in which they are unitied (Appelt (1989)). Writing reversible grammars, however, presents problems which do not arise in the traditional grammars used for either analysis or generation. In addition, the progress accomplished recently in building generators for unification grammars has already revealed some of the problems posed by unificationbased reversible grammars. 2 As shown by Russell et al. (1990), even though the grammar rules do not refer to the generation process, the generation algorithm imposes particular constraints on the grammar formalism. 3 This paper concentrates particularly on the problems encountered in the generation of French, specifically in the analysis to be given to clitics.