Hierarchical approaches to machine translation have proven increasingly successful in recent years (Chiang, 2005;Marcu et al., 2006;Shen et al., 2008), and often outperform phrase-based systems (Och and Ney, 2004;Koehn et al., 2003) on target-language fluency and adequacy.
their benefits generally come with high computational costs, particularly when chart parsing, such as CKY, is integrated with language models of high orders (Wu, 1996).