GUS, A Frame-Driven Dia|og System


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ARTIFICIAL INTELLIGENCE 155 GUS, A Frame-Driven Dia|og System Daniel G. Bobrow, Ronald M. Kaplan, Martin Kay, Donald A. Norman, Henry Thompson and Terry Winograd Xerox Palo Alto Research Center, 3333 Coyote Hill Road, Palo Alto, CA 94304, U.S.A. Recommended by Don Walker ABSTRACT GUS is the first of a series of experimental computer systems that we intend to construct as part of a program of research on language understanding. In large measure, these systems will fill the role o f periodic progress reports, summarizing what we have learned, assessing the mutual coherence of the various lines of investigation we have been following, and saggestin# where more emphasis is needed in future work. GUS (Genial Understander System) is intended to engage a sympathetic and highly cooperative human in an English dialog, directed towards a specific goal within a very restricted domain of discourse. As a starting point, G US was restricted to the role of a travel agent in a con- versation with a client who wants to make a simple return trip to a single city in California. There is good reason for restricting the domain of discourse for a computer system which is to engage in an English dialog. Specializing the subject matter that the system can talk about permiis it to achieve some measure of realism without encompassing all the possibilities of human knowledge or o f the English language. It also provides the user with specific motivation for participating in the conversation, thus narrowing the range of expectations that GUS must have about the user's pur- poses. A system restricted in this way will be more able to guide the conversation within the boundaries o f its competence. 1. Motivation and Design Issues Within its limitations, ous is able to conduct a more-or-less realistic dialog. But the outward behavior of this first system is not what makes it interesting or signifi- cant. There are, after all, much more convenient ways to plan a trip and, unlike some other artificial intelligence programs, (;us does not offer services or furnish information that are otherwise difficult or impossible to obtain. The system is i nteresting because of the phenomena of natural dialog that it attempts to model tThis work was done by the language understander p oject at the Xerox Palo Alto Research center. Additional affiliations: D. A. Norman, University of California, San Diego; H. Thompso6, University of California, Berkeley; and T. Winograd, Stanford University. Artificial Intelligence 80977), 155-173 Copyright © 1977 by North-Holland Publishing Company 156 D.G. BOBI~OW ET AL. and because of the principles of program organization around which it was de, Signed. Among the hallmarks of natural dialogs are unexpected and seemingly un- predictable sequences of events. We describe some of the forms that these can take below. "We then go on to discuss the modular design which makes the system re!atively insensitive to the vagaries of ordinary conversation. 1.1. Problems of natural dialog The simple dialog shown in Fig. 1 illustrates ome of the language-understanding problems ...

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