Recent works for Open-domain Question Answering refer to an external knowledge base using a retriever model, optionally rerank the passages with a separate reranker model and generate an answer using an another reader model. Despite performing related tasks, the models have separate parameters and are weakly-coupled during training. In this work, we propose casting the retriever and the reranker as hard-attention mechanisms applied sequentially within the transformer architecture and feeding the resulting computed representations to the reader. In this singular model architecture the hidden representations are progressively refined from the retriever to the reranker to the reader, which is more efficient use of model capacity and also leads to better gradient flow when we train it in an end-to-end manner. We also propose a pre-training methodology to effectively train this architecture. We evaluate our model on Natural Questions and TriviaQA open datasets and for a fixed parameter budget, our model outperforms the previous state-of-the-art model by 1.0 and 0.7 exact match scores.

本研究提出了一种基于transformer架构的内部逐层注意力机制，将知识库搜索模型和重排模型整合为统一的模型，并进行端到端训练，以实现高效利用模型容量并提高梯度流量。该模型可以在固定参数预算内显著优于现有模型，达到1.0和0.7的精准匹配得分。

开放域问答只需一个模型