Dialogue Models for Inquiry and Transaction

Abstract Designing and testing a usable dialogue system is still considered an art. Usability is arguably the most important quality factor for dialogue systems. In order to design and test a system, one needs to relate the properties of a dialogue design to verifiable properties of the resulting dialogues. For dialogue systems, usability can be expressed as a combination of effectiveness and efficiency with respect to the underlying task, and a number of properties that are related to coherence. To express these properties, we study formal models of dialogue. The coherence of an utterance with respect to the dialogue context depends on its form, on its content, and on its function in relation to the task and the interaction process. How to combine these aspects in one framework? Following work by Clark, we argue that a dialogue can be seen as a combination of joint actions that are coordinated at various linguistic levels. With respect to the content, information is conceived of as structured by issues: questions that are currently under discussion. Dialogues for inquiry, cooperative information exchange, can thus be modelled as a constant process of raising and resolving issues. An utterance is called relevant, when its content resolves one of the current issues. Other content-related coherence constraints are consistency, informativeness and licensing: not being over-informative. A transaction is the result of a number of negotiation phases: opening, exchanging information, exchanging proposals, confirmation and closure. A logic that specifies agents in terms of their beliefs, preferences and commitments is used to model the negotiation task. The coherence of the interaction process can be described by the rules of a dialogue game. These aspects are related. We argue that dialogue games are recipes for joint action. Some results of the design, implementation and evaluation effort of three particular dialogue system applications are discussed.

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Defended 7th of April, 2000, University of Twente. Supervised by prof.dr. Anton Nijholt.