In this paper, Finite-State-Automata (FSA) and theorem-proving approaches to spoken dialogue systems (SLDS) are contrasted to each other. FSA are too rigid to deal with unpredictable user reactions, such as corrections or counter-questions, whereas planbased approaches are usually too complex to be effectively used, given the unreliability of word recognition and the elliptical and unconventional nature of spontaneous speech. As an alternative, a Dialogue Manager architecture is proposed which uses knowledge on both the possible sequences of dialogue acts and the dynamic representation of the task and requirements for its fulfillment. The behaviour of the specific user is taken into consideration, including their expectations about the system and the service offered, as are instances of miscommunication and disagreement in the course of the dialogue, and the successful completion of sub-plans relevant to the task and the dialogue flow
