In recent years, statistical machine translation(SMT) has been rapidly developing with more and more novel translation models being proposed and put into practice (Koehn et al., 2003;Och and Ney, 2004;Galley et al., 2006;Liu et al., 2006;Chiang, 2007;Chiang, 2010).
similar to other natural language processing(NLP) tasks, SMT systems often suffer from domain adaptation problem during practical applications.