Dense retrieval approaches can overcome the lexical gap and lead to significantly improved search results. However, they require large amounts of training data which is not available for most domains. As shown in previous work (Thakur et al., 2021b), the performance of dense retrievers severely degrades under a domain shift. This limits the usage of dense retrieval approaches to only a few domains with large training datasets. In this paper, we propose the novel unsupervised domain adaptation method Generative Pseudo Labeling (GPL), which combines a query generator with pseudo labeling from a cross-encoder. On six representative domain-specialized datasets, we find the proposed GPL can outperform an out-of-the-box state-of-the-art dense retrieval approach by up to 8.9 points nDCG@10. GPL requires less (unlabeled) data from the target domain and is more robust in its training than previous methods. We further investigate the role of six recent pre-training methods in the scenario of domain adaptation for retrieval tasks, where only three could yield improved results. The best approach, TSDAE (Wang et al., 2021) can be combined with GPL, yielding another average improvement of 1.0 points nDCG@10 across the six tasks.

该研究论文提出了一种新的无监督领域适应方法Generative Pseudo Labeling，该方法结合查询生成器和交叉编码器的伪标记，证明该方法可以在数据集较小的目标领域中进行更加鲁棒的训练，并且在检索任务上比最先进的密集检索方法提高了近9.3个百分点的nDCG@10指标。

GPL: 密集检索的生成伪标签用于无监督域适应