More specifically, the probability could be estimated by the maximum likelihood (MLE) approach, Given a phrase pair f , e and word alignment a, and the dependent relation of the source sentence d J 1 (J is the length of the source sentence, I is the length of the target sentence).
given the lexical translation probability distribution p(e|f → f ′ ), we compute the feature score of a phrase pair (f , e) as represents dependent relation of the target side) in the similar way.