sentence1: word alignment is a critical component in training statistical machine translation systems and has received a significant amount of research , for example , ( cite-p-17-1-0 , cite-p-17-1-8 , cite-p-17-1-4 ) , including work leveraging syntactic parse trees , e.g. , ( cite-p-17-1-1 , cite-p-17-1-2 , cite-p-17-1-3 ) .
sentence2: word alignment is the task of identifying translational relations between words in parallel corpora , in which a word at one language is usually translated into several words at the other language ( fertility model ) ( cite-p-18-1-0 ) .