“…Task-oriented dialogue systems are primarily designed to search and interact with large databases which contain information pertaining to a certain dialogue domain: the main purpose of such systems is to assist the users in accomplishing a welldefined task such as flight booking (El Asri et al, 2017), tourist information (Henderson et al, 2014), restaurant search (Williams, 2012), or booking a taxi (Budzianowski et al, 2018). These systems are typically constructed around rigid task-specific ontologies (Henderson et al, 2014;Mrkšić et al, 2015) which enumerate the constraints the users can express using a collection of slots (e.g., PRICE RANGE for restaurant search) and their slot values (e.g., CHEAP, EXPENSIVE for the aforementioned slots).…”