Inherit or discard: learning better domain-specific child networks from the general domain for multi-domain NMT

Multi-domain NMT aims to develop a parameter-sharing model for translating general and specific domains, such as biology, legal, etc., which often struggle with the parameter interference problem. Existing approaches typically tackle this issue by learning a domain-specific sub-network for each domain equally, but they ignore the significant data imbalance problem across domains. For instance, the training data for the general domain often outweighs the biological domain tenfold. In this paper, we observe a natural similarity between the general and specific domains, including shared vocabulary or similar sentence structure. We propose a novel parameter inheritance strategy to adaptively learn domain-specific child networks from the general domain. Our approach employs gradient similarity as the criterion for determining which parameters should be inherited or discarded between the general and specific domains. Extensive experiments on several multi-domain NMT corpora demonstrate that our method significantly outperforms several strong baselines. In addition, our method exhibits remarkable generalization performance in adapting to few-shot multi-domain NMT scenarios. Further investigations reveal that our method achieves good interpretability because the parameters learned by the child network from the general domain depend on the interconnectedness between the specific domain and the general domain.