In the MSD model, during the phrase extraction, given a source sentence S and a target sentence T , the alignment set A, where a j i is an alignment from i to j, the phrase pair with words in positions between i and j in S, S j i , and n and m in T , T m n , can be classified with one of three orientations with respect to the previous word: • The orientation is monotonous if only the previous word in the source is aligned with the previous word in the target, or, more formally, if a n−1 i−1 ∈ A ∧ a n−1 j+1 / ∈ A.
the relationship between the word alignment quality and the results is not straightforward, and it was shown in (Vilar et al., 2006) that better alignments in terms of F-measure do not always lead to better translation quality.