“…One approach is a hierarchical architecture composed of several agents. They use a classifier to select the right agent for each utterance (Coronado et al, 2015;Banchs et al, 2013;Planells et al, 2013;Pichl et al, 2018) or a ranking approach that generates answers by each DS and then selects the best answer (Song et al, 2018;Tanaka et al, 2019;Paranjape et al, 2020). Other approaches use a joint architecture to solve multiple dialog tasks (Lewis et al, 2020;Shuster et al, 2020).…”