Machine Translation Based on Constraint-Based Synchronous Grammar

This paper proposes a variation of synchronous grammar based on the formalism of context-free grammar by generalizing the first component of productions that models the source text, named Constraint-based Synchronous Grammar (CSG). Unlike other synchronous grammars, CSG allows multiple target productions to be associated to a single source production rule, which can be used to guide a parser to infer different possible translational equivalences for a recognized input string according to the feature constraints of symbols in the pattern. Furthermore, CSG is augmented with independent rewriting that allows expressing discontinuous constituents in the inference rules. It turns out that such grammar is more expressive to model the translational equivalences of parallel texts for machine translation, and in this paper, we propose the use of CSG as a basis for building a machine translation (MT) system for Portuguese to Chinese translation.