A Framework for Describing Mental States and Their Dynamic Changes of Dialog Participants

Abstract

In order to make a dialog system cooperative, it needs to have a framework of describing beliefs of the partner (user) who converses with it. Because such descriptions contain beliefs of the system, itself, the entire belief description structure is nested. This paper proposes a framework in which we can describe both the participants' mental states and their dynamic changes during the dialog. Previous research on formalizing speech acts often define operators that correspond to each speech act. All these operators are defined in terms of preconditions and effects, and they are combined to make a sequence of speech acts. With these operators, however, it is not easy to show the course of overall dialog. This formalization is not powerful enough for making dialog cooperative, such as helping the partner to achieve his goal that is not specified during the dialog. In our framework, some constructs are employed to express the mental states. Some of the speech acts, such as informing and requesting, are regarded as manipulations on the constructs in our nested belief structure. These speech acts correspond to the addition of constructs from outer layers to inner layers in the nested belief structure. New construct "HOLE" is introduced to express the lack of belief. It enables us to handle both informing and requesting in the same manner, and to express the goal state of the dialog explicitly. The new construct also enables us to describe a strategy for making responses cooperative. With this framework, we can clearly express various phenomena of conveying propositions and intentions in terms of dynamic changes of belief descriptions.