Introduction

Planning and plan recognition have been identified as mechanisms for the generation and understanding of dialogues. Founded on speech act theory [6] [65], and Grice's theory of meaning [27], a body of research has developed that views cooperative dialogue as a joint activity of generation of acts by a speaker, and then plan recognition and response by the hearer [10]. It was soon realised that in this process, different belief sets are involved [53]. The speaker's beliefs are used in the generation part, whereas the hearer's beliefs are used in plan recognition, and generation of a cooperative response. To plan a dialogue of many steps, a deeply nested belief model is required, whereby one agent may generate an expectation of the other's dialogue contribution by estimating its beliefs.