Unsupervised Pivot Translation for Distant Languages
Table 3: The performance of different routing methods. The BLEU score is averaged on all the distant language pairs in the test set. The compared methods include: DT: direct unsupervised translation, RR: random routing, PP: prior pivoting, HA: hop average, LTR: our proposed learning to route, and GT: the best translation path (the ground truth).
['Methods', '[ITALIC] DT', '[ITALIC] RR', '[ITALIC] HA', '[ITALIC] PP', '[ITALIC] LTR', '[ITALIC] GT']
The small gap between the ground truth and LTR demonstrates that although LTR fails to select the best path in 43% of the distant pairs (just 57% in terms of top-1 accuracy), it indeed chooses the path which has a BLEU score slightly lower than the best path. Random routing (RR) even performs worse than DT, demonstrating the routing problem is non-trivial. LTR outperforms PP and HA by more than 1 BLEU point on average.