Translation Rules with Right-Hand Side Lattices

In Corpus-Based Machine Translation, the search space of the translation candidates for a given input sentence is often defined by a set of (cyclefree) context-free grammar rules. This happens naturally in Syntax-Based Machine Translation and Hierarchical Phrase-Based Machine Translation (where the representation will be the set of the target-side half of the synchronous rules used to parse the input sentence). But it is also possible to describe Phrase-Based Machine Translation in this framework. We propose a natural extension to this representation by using lattice-rules that allow to easily encode an exponential number of variations of each rules. We also demonstrate how the representation of the search space has an impact on decoding efficiency, and how it is possible to optimize this representation.