Aligning sentences in parallel corpora

Abstract

In this paper we describe a statistical technique for aligning sentences with their translations in two parallel corpora. In addition to certain anchor points that are available in our da.ta, the only information about the sentences that we use for calculating alignments is the number of tokens that they contain. Because we make no use of the lexical details of the sentence, the alignment computation is fast and therefore practical for application to very large collections of text. We have used this technique to align several million sentences in the English-French Hanstrd corpora and have achieved an accuracy in excess of 99% in a random selected set of 1000 sentence pairs that we checked by hand. We show that even without the benefit of anchor points the correlation between the lengths of aligned sentences is strong enough that we should expect to achieve an accuracy of between 96% and 97%. Thus, the technique may be applicable to a wider variety of texts than we have yet tried.