Constraint-driven Grammar Description
Résumé
For a large number of applications in Natural Language Processing (NLP) (e.g., Dialogue Systems, Automatic Summarisation, Machine-Translation, etc.), one needs a fine-grained description of language. By fine-grained, it is generally meant that this description should precisely define the relations between the constituents of the sentence (often referred to as deep syntactic description), and, also, when possible, contain information about the meaning of the sentence (semantic representation). For such a fine-grained description of language to be processed by a computer, it is usually encoded in a mathematical framework called Formal Grammar. Here, we will consider three grammar formalisms whose expressivity lies beyond that of CFG making them suitable for the description of the syntax of several natural languages. These formalisms are Tree-Adjoining Grammar (TAG), Lexical Functional Grammar (LFG) and Property Grammar (PG). They have been used to describe several electronic grammar for e.g. English (XTAG Research Group, 2001), Chinese (Fang and King, 2007), or French (Prost, 2008). TAG will serve as a basis for illustrating one of the main issues raised when developing real-size grammatical resources, namely redundancy. Redundancy is the fact that grammar rules often share significant common substructures. This redundancy greatly impacts grammar development and maintenance (how to ensure coherence between grammar rules?). LFG and PG will serve as support formalisms in the context of cross- framework grammar engineering.