Dialog Control in a Natural Language System

Dialog Control in a Natural Language System 1 Michael Gerlach Helmut Horacek Universit~t Hamburg Fachbereich Informatik Projektgruppe WISBER Jungiusstra6e 6 D-2000 Hamburg 36 F.R.G. ABSTRACT In this paper a method for controlling the dialog in a natural language (NL) system is presented. It provides a deep modeling of information processing based on time dependent propositional attitudes of the interacting agents. Knowledge about the state of the dialog is represented in a dedicated language and changes of this state are described by a compact set of rules. An appropri- ate organization of rule application is introduced including the initiation of an adequate system reaction. Finally the application of the method in an NL consultation system is outlined. INTRODUCTION The solution of complex problems fre- quently requires cooperation of multi- ple agents. A great deal of interaction is needed to identify suitable tasks whose completion contributes to attaining a common goal and to organize those tasks appropriately. In particular, this involves carrying out communicative subtasks including the transfer of knowledge, the adjustment of beliefs, expressing wants and pursuing their satisfaction, all of which is motivated by the intentions of the interacting agents [Werner 88]. An ambitious dia- log system (be it an interface, a mani- pulation system, or a consultation sys- tem) which is intended to exhibit (some of) these capabilities should therefore consider these intentions in processing 1 The work described in this paper is part of the joint project WISBER, which is sup- ported by the German Federal Ministery for Research and Technology under grant ITW- 8502. The partners in the project are: Nixdorf Computer AG, SCS Orbit GmbH, Siemens AG, the University of Hamburg, and the Uni- versity of SaarbrOcken. the dialog, at least to the extent that is required for the particular type of the dialog and the domain of application. A considerable amount of work in cur- rent AI research is concerned with in- ferring intentions from utterances (e.g., [Allen 83], [Carberry 83], [Grosz, Sidner 86]) or planning speech acts serving certain goals (e.g., [Appelt 85]), but only a few uniform approaches to both as- pects have been presented. Most approaches to dialog control de- scribed in the literature offer either rigid action schemata that enable the simulation of the desired behavior on the surface (but lack the necessary de- gree of flexibility, e. g., [Metzing 79]), or descriptive methods which may also in- clude possible alternatives for the con- tinuation of the dialog, but without ex- pressing criteria to .~aide an adequate choice among them (e. g., [Me~ing et al. 87], [Bergmann, Gerlach 87]). Modeling of beliefs and intentions (i.e., of propositional attitudes) of the agents involved is found only in the ARGOT system [Litman, Allen 84]. This ap- proach behaves sufficiently well in se- veral isolated situations, but it fails to demonstrate a continuously adequate behavior in the course of a complete dia- log. An elaborated theoretical frame- work is provided in [Cohen, Perrault 79] but they explicitly exclude the dele- tion of propositional attitudes. …

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