where x j and x e are respectively the Japanese and English word n-grams, f (x j ) and f (x e ) are respectively the appearance frequencies of x j and x e in the parallel corpora, and f (x j , x e ) is the frequency of x j and x e co-occurring in the same pairs of Japanese-English sentences.
the similarity between the Japanese and English word n-grams in each pair extracted in step (1) is computed, and a pair is considered a pair of parallel translation expressions if the similarity is larger than a threshold value.