As a general basis for constructing a cooperative and flexible dialogue system, we are interested in modelling the inference process of an agent who participates in a dialogue. For this purpose, it is natural and powerful to model it in his general cognitive framework for problem solving. This paper presents such a framework. In this framework, we represent agent's mental states in the form called Mental World Structure, which consists of multiple mental worlds. Each mental world is a set of mental propositions and corresponds to one modal context, that is, a specific point of view. Modalities in an agent's mental states are represented by path expressions, which are first class citizens of the system and can be composed each other to make up composite modalities. With Mental World Structure, we can handle modalities more flexibly than ordinary modal logics, situation theory and other representation systems. We incorporate smoothly into the structure three basic inference procedures, that is, deduction, abduction and truth maintenance. Precise definitions of the structure and the inference procedures are given. Furthermore, we explain as examples, several cooperative dialogues in our framework.

This system called COKIS automatically extracts knowledge about C functions from the UNIX on-line manual by using its description paragraph and the user can interactively inquire to the system in order to know about UNIX C functions. The idea is motivated on the one side to free users from being involved in an exhaustive knowledge acquisition in the past, and to examine problems in understanding knowledge itself on the other. We propose Memory Processor which is implemented to realize extracting knowledges from corpus and processing dialogues in the inquiry system at the same modules.