Recent work on open-domain question answering largely follow this retrieve-and-read approach, and focus on improving the information retrieval component with question answering performance in consideration (Nishida et al., 2018;Kratzwald and Feuerriegel, 2018;Nogueira et al., 2019).
span offset scores are predicted from each paragraph independently before finally aggregated and normalized with a global softmax operation to produce probabilities over spans.