1. INTRODUCTION
Task-oriented dialogues (TOD) are very common in our daily lives, such as the moment when we book a hotel or a restaurant reservation. Dialogue State Tracking (DST) task is crucial in current TOD systems [1], [2]. Its goal is to understand the user’s requirement given the dialogue history under a domain ontology. For example, there is a restaurant reservation in Figure 1. The system should find out the user’s requirements regarding the restaurant. The belief state denotes the domain-slot-value triples of the dialogue history.