With the rise of deep learning approaches, several neural belief trackers (NBT) have been proposed and improved the performance by learning semantic neural representations of words Mrkšić and Vulić, 2018).
the scalability still remains as a challenge; the previously proposed methods either individually model each domain and/or slot (Zhong et al., 2018;Ren et al., 2018;Goel et al., 2018) or have difficulty in adding new slot-values that are not defined in the ontology Nouri and Hosseini-Asl, 2018).