User Models: The Problem of Disparity

USER MODELS: THE PROBLEM OF DISPARITY Sandra Carberry I)epartment of Computer and Information Sciences University of Delaware Newark, Delaware 19716, U.S.A. ABSTRACT A signific~mt component of a user raodel in au infornration-seeking dialogue is tim task-related plazl motivating the information-seeker's queries. A number of researchers have Irmdeled the plan inference process and used these models to design more robust natural language interfaces. However in each case, it has been assumed that the system's context model and the plan under construction by the information-seeker are never at variance. This paper addre~es the problem of disparate plans. It presents a four phase approach and argues that hmldling disparate plans requires an enriched context model. This model nmst permit tile addition of companents suggested by the information- ,'~eeker but not fully supported by the system's domain knowledge, and must differentiate mnong its com- ponents according to the kind of support accorded each component as a correct part of the information-seeker's overall plan. It is shown how a component's support should affect the system's hypothesis about the source of error once plan disparity is suggested. I. INTRODUCTION Corranunication as we know it involves more thml ~inlply answering isolated queries. When two individuals participate in an iuformation-seeking dialogue, tile information-provider uses the context within which each query occurs to interpret the query, determine tile desired information, and formulate an appropriate response. This context consists of more than mere knowledge of the previous questions and answers. A cooperative participant uses the information exchanged during the dialogue and knowledge of the domain to hypothesize a model of the speaker; this model is adjusted and expanded as the dialogue progresses and is called a user model. Perhaps the most significant component of a user model is the listener's belief about the underlying task motivating the information-seeker's queries and his partially developed plan for accomplishing this task. A number of researchers have modeled the plan inference process [Allen 1980], [Cacberry 1983], [Grosz 1977], [Litman 1984], [Perrault 19801, [Robinson 1981], [Sidner 1983], and these models have been used to understand indirect speech acts [Perranlt 1980], provide helpful responses [Allen 1980], interpret pragmatically ill-formed queries [Carberry 1986], under- stand intersentential ellipsis [Allen 1980, Carberry 1985], and iden- tify the kind of response intended by a speaker [Sidner 1983]. However in each case, four critical assmnptions have been magic: [1] Tile inforroation-seeker's knowledge about the task domain may be lacking but is not erroneous. [2] The infornmtion-seeker's queries never address aspects of the task outside tile system's knowledge. Such systems maintain the closed world assumption [Reiter 1978]. [3] The information provided by the information-seeker is correct a~ld not misleading. [4] The underlying plan inferred by the system prior to analysis of a new utterance is a partially instantiated version of the plan under consideration by the information-seeker. These assumptions eliminate the possibility that tile information- seeker might ask queries irrelevant to the task at hand, that the information..seeker might ask about details outside tile system's limited knowledge, that the information-seeker might accidentally …

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