The representation and use of focus in a system for understanding dialogs

THE REPRESENTATION AND USE OF FOCUS IN A SYSTEM FOR UNDERSTANDING DIALOGS Barbara J. Grosz Artificial Intelligence Center SRI International, Menlo Park, California 94025 ABSTRACT As a dialog progresses the objects and actions that are most relevant to the conversation, and hence in the focus of attention of the dialog participants, change. This paper describes a representation of focus for language understanding systems, emphasizing its use in understanding taskoriented dialogs. The representation highlights that part of the knowledge base relevant at a given point in a dialog. A model of the task is used both to structure the focus representation and to provide an index into potentially relevant concepts in the knowledge base The use of the focus representation to make retrieval of items from the knowledge base more efficient is described. I INTRODUCTION To understand the sentences in a discourse, a computer system, like a person, must have knowledge about the domain of the discourse. However, the knowledge required to understand even simple, reallife domains is so extensive that it will overwhelm a system that does not apply it selectively. This means that the ability to focus on the subset of knowledge relevant to a particular situation is crucial. This paper addresses the problem of focus from the perspective of building a computer system that can participate in a task-oriented dialog. A representation for focus is presented; its use is illustrated by showing how the referents of definite noun phrases are identified. A combination of contextual factors influences the interpretation of an utterance. In fact, what is usually meant by "the context of an utterance" is precisely that set of constraints which together direct attention to the concepts of interest in the discourse in which the utterance occurs. Both the preceding discourse context - - the utterances that have already occurred -- and the situational context -- the environment in which an utterance occurs -- affect the interpretation of the utterance. For a dialog, the situational context includes the physical environment, the social setting, and the relationship between the participants in the dialog. This paper shows how the task and dialog contexts combine to provide a focus on those concepts relevant to the interpretation of utterances in task-oriented dialogs.