The study considered word alignments both in isolation and in combination with independently generated parse trees for one or both sentences in each pair.
the study is relevant to finite-state phrase-based models that use no parse trees (Koehn et al., 2003), tree-tostring models that rely on one parse tree (Yamada and Knight, 2001), and tree-to-tree models that rely on two parse trees (Groves et al., 2004, e.g.).