The choice of modelling P (φ(x, a, y)|x) instead of modelling P (y|x) directly is crucial, both from a modelling and from a computational perspective.
second, using a heuristic proposed in (Och et al., 1999), all the aligned phrase pairs (x , a , y ) satisfying the following criteria are extracted: (1) x and y consist of consecutive words of x and y, and both have length at most k, (2) a is the alignment between words of x and y induced by a, (3) a contains at least one link, and (4) there are no links in a that have just one end in x or y .