For the first issue, a number of models have been proposed to model the structure mapping between tree and string (Galley et al., 2004;Liu et al., 2006;Yamada and Knight, 2001;DeNeefe and Knight, 2009) and between tree and tree (Eisner, 2003;Zhang et al., 2007Zhang et al., & 2008Liu et al., 2009).
mapping from tree-to-tree sequence into tree-to-string rule In this subsection, we describe what the parallel search spaces are and how to construct them.