Recognizing complex discourse acts: a tripartite plan-based model of dialogue
Lynn Lambert · 1993
Current natural language understanding systems are severely limited in their handling of many kinds of dialogues. They handle each utterance in relative isolation, with little or no use of the established dialogue context, of general knowledge of the world, of the system's beliefs about the user's beliefs, or of the linguistic information contained in the user's utterances. Consequently, current systems are unable to recognize when a user is conveying lack of belief in the system's claims or conveying implicit acceptance of previously communicated propositions. These shortcomings prevent these systems from being able to recognize complex communicative actions such as expressing doubt, and subsequent actions which implicitly indicate acceptance of communicated propositions. This thesis presents a tripartite model of dialogue that overcomes these limitations. The model distinguishes among domain, problem-solving, and discourse or communicative actions, thus capturing a wider range of goals than previous models. It is able to recognize the role of utterances even when that role cannot be identified from a single utterance alone. The thesis shows how people convey uncertain beliefs by the surface form of their utterances and argues that recognition of complex discourse acts requires a multi-strength belief model capable of representing such beliefs. It presents an algorithm that combines world, linguistic, and contextual knowledge to recognize complex discourse acts such as expressing doubt and that enables the system to model the structure of negotiation dialogues. As a result, this model is a step towards a complete model of negotiation and thus a more robust model of understanding.