This fact suggests that a dialog system should be also capable of conducting multi-topic conversations with users to provide them a more natural interaction with the system.
the other direction of dialog topic tracking approaches made use of external knowledge sources including domain models (Roy and Subramaniam, 2006), heuristics (Young et al., 2007), and agendas (Bohus and Rudnicky, 2003;Lee et al., 2008).