Finally, when used as an additional model in the log-linear framework of phrase-based decoding, an n-gram model trained on JTR sequences introduces only one single feature to be tuned, whereas the OSM additionally uses 4 supportive features (Durrani et al., 2013b).
the RNN scores are computed using approximations instead (Auli et al., 2013;Alkhouli et al., 2015).