Following Och and Ney (2002), we depart from the traditional noisy-channel approach and use a more general log-linear model over derivations D: where the φ i are features defined on derivations and the λ i are feature weights.
one of the features is an m-gram language model P LM (e); the remainder of the features we will define as products of functions on the rules used in a derivation: we can rewrite P(D) as The factors other than the language model factor can be put into a particularly convenient form.