Some encoder inputs such as conversation histories are frequently extended with short additional inputs like new responses. However, to obtain the real-time encoding of the extended input, existing Transformer-based encoders like BERT have to encode the whole extended input again without utilizing the existing encoding of the original input, which may be prohibitively slow for real-time applications. In this paper, we introduce Incremental Transformer, an efficient encoder dedicated for faster encoding of incremented input. It takes only added input as input but attends to cached representations of original input in lower layers for better performance. By treating questions as additional inputs of a passage, Incremental Transformer can also be applied to accelerate MRC tasks. Experimental results show tiny decline in effectiveness but significant speedup against traditional full encoder across various MRC and multi-turn conversational question answering tasks. With the help from simple distillation-like auxiliary losses, Incremental Transformer achieves a speedup of 6.2x, with a mere 2.2 point accuracy reduction in comparison to RoBERTa-Large on SQuADV1.1.

Temporal language grounding (TLG) aims to localize a video segment in an untrimmed video based on a natural language description. To alleviate the expensive cost of manual annotations for temporal boundary labels,we are dedicated to the weakly supervised setting, where only video-level descriptions are provided for training. Most of the existing weakly supervised methods generate a candidate segment set and learn cross-modal alignment through a MIL-based framework. However, the temporal structure of the video as well as the complicated semantics in the sentence are lost during the learning. In this work, we propose a novel candidate-free framework: Fine-grained Semantic Alignment Network (FSAN), for weakly supervised TLG. Instead of view the sentence and candidate moments as a whole, FSAN learns token-by-clip cross-modal semantic alignment by an iterative cross-modal interaction module, generates a fine-grained cross-modal semantic alignment map, and performs grounding directly on top of the map. Extensive experiments are conducted on two widely-used benchmarks: ActivityNet-Captions, and DiDeMo, where our FSAN achieves state-of-the-art performance.

The ability to ask clarification questions is essential for knowledge-based question answering (KBQA) systems, especially for handling ambiguous phenomena. Despite its importance, clarification has not been well explored in current KBQA systems. Further progress requires supervised resources for training and evaluation, and powerful models for clarification-related text understanding and generation. In this paper, we construct a new clarification dataset, CLAQUA, with nearly 40K open-domain examples. The dataset supports three serial tasks: given a question, identify whether clarification is needed; if yes, generate a clarification question; then predict answers base on external user feedback. We provide representative baselines for these tasks and further introduce a coarse-to-fine model for clarification question generation. Experiments show that the proposed model achieves better performance than strong baselines. The further analysis demonstrates that our dataset brings new challenges and there still remain several unsolved problems, like reasonable automatic evaluation metrics for clarification question generation and powerful models for handling entity sparsity.