For conversion from PS to DS, a head-table approach (Magerman, 1994;Collins, 2003;Yamada and Matsumoto, 2003;Sun and Jurafsky, 2004;Nivre, 2006;Johansson and Nugues, 2007;Duan et al., 2007;Zhang and Clark, 2008) is widely used.
the reliability of head tables has been questioned (Xue, 2007).