CAT-BERT: A Context-Aware Transferable BERT Model for Multi-turn Machine Reading Comprehension.

Machine Reading Comprehension (MRC) is an important NLP task with the goal of extracting answers to user questions from background passages. For conversational applications, modeling the contexts under the multi-turn setting is highly necessary for MRC, which has drawn great attention recently. Past studies on multi-turn MRC usually focus on a single domain, ignoring the fact that knowledge in different MRC tasks are transferable. To address this issue, we present a unified framework to model both single-turn and multi-turn MRC tasks which allows knowledge sharing from different source MRC tasks to help solve the target MRC task. Specifically, the Context-Aware Transferable Bidirectional Encoder Representations from Transformers (CAT-BERT) model is proposed, which jointly learns to solve both single-turn and multi-turn MRC tasks in a single pre-trained language model. In this model, both history questions and answers are encoded into the contexts for the multi-turn setting. To capture the task-level importance of different layer outputs, a task-specific attention layer is further added to the CAT-BERT outputs, reflecting the positions that the model should pay attention to for a specific MRC task. Extensive experimental results and ablation studies show that CAT-BERT achieves competitive results in multi-turn MRC tasks, outperforming strong baselines.