The Edit Distance Transducer in Action: The University of Cambridge English-German System at WMT16
Table 2: Projection methods on news-test2016 with NMT 8-ensemble.
['[BOLD] Method', '[BOLD] BLEU']
First, we focus on the projection function ΠUNK(⋅) which switches between preserving the input and output label at the UNK symbol to produce the combined translation ˆtcomb (Eq. As explained in Sec. Tab. Remarkably, using the ˆtHiero translations results in 30.4 BLEU, which is a very substantial improvement over the baseline Hiero system (26.0 BLEU). Note that this BLEU score is achieved with hypotheses from the original Hiero lattice H but weighted in combination with the NMT scores and the edit distance. However, these selected paths are often given very low scores by Hiero: in only 8.6% of the sentences is the Hiero hypothesis left unchanged. This indicates the benefit in using lattice-based approaches over n-best lists.