Improving Lexical-Constraint-Aware Machine Translation by Factoring Encoders

Existing lexically constrained machine translation employs data augmentation and incorporates lexical constraints during decoding period, which requires a bilingual dictionary or costs much decoding time. In this paper, we propose a simple but effective method to leverage lexical constraints. We use separate encoders to encode source sentence and lexical constraints, with self-attention layer mask to disentangle the two encoding subtasks. Our method does not require bilingual dictionaries or modify decoding process. Experiments on WMT 2016 English-German (En-De) and IWSLT 2017 English-Chinese (En-Zh) datasets show that our method gains improvement compared to baseline models.