Extractive Question Answering with Dynamic Query Representation for Free

Extractive QA is an important NLP task with numerous real-world applications. The most common method for extractive QA is to encode the input sequence with a pretrained Transformer such as BERT, and then compute the probability of the start and end positions of span answers using two leaned query vectors. This method has been shown to be effective and hard to outperform. However, the query vectors are static, meaning they are the same regardless of the input, which can be a challenging issue in improving the model's performance. To address this problem, we propose \texttt{DyReF} (\texttt{Dy}namic \texttt{Re}presentation for \texttt{F}ree), a model that dynamically learns query vectors for free, i.e. without adding any parameters, by concatenating the query vectors with the embeddings of the input tokens of the Transformer layers. In this way, the query vectors can aggregate information from the source sentence and adapt to the question, while the representations of the input tokens are also dependent on the queries, allowing for better task specialization. We demonstrate empirically that our simple approach outperforms strong baseline in a variety of extractive question answering benchmark datasets. Our code will be made publicly available.