The problem of modeling human understanding and generation of a coherent dialog is investigated by simulating a conversation participant. The rule-based system currently under development attempts to capture the intuitive concept of "topic" using data structures consisting of declarative representations of the subjects under discussion linked to the utterances and rules that generated them. Scripts, goal trees, and a semantic network are brought to bear by general, domain-independent conversational rules to understand and generate coherent topic transitions and specific output utterances. .
