Since reordering in phrase-based and word-based models leads to an exponential growth of the search space, reordering constraints are introduced for efficient decoding.
Reordering Constraints is the main subject of 10 publications.
Matusov et al. (2005)
constrain reordering when the input word sequence was consistently translated monotone in the training data. Zens and Ney (2003)
; Zens et al. (2004)
; Kanthak et al. (2005)
compare different reordering constraints and their effect on translation performance, including the formal grammar ITG constraint, which may be further restricted by insisting on a match to source side syntax (Yamamoto et al., 2008)
Similarly, reordering may be restricted to syntactically cohesion (Cherry, 2008)
. Ge et al. (2008)
integrate other linguistically inspired reordering models into a phrase-based decoder. Dreyer et al. (2007)
compare reordering constraints in terms of oracle BLEU, i.e., the maximum possible BLEU score. Goh et al. (2011)
use constraints based on part-of-speech patterns mostly along clause boundaries to improve Japansese-English patent translation.
Instead of hard limits on reordering, reordering models may inform search.