Refinement of Intentions

The aim of this paper is to provide a logical analysis of intention refinement process which plays a fundamental role in the belief-desire-intention (BDI) theory. We briefly show the existing results: a logical framework for intention refinement and the extension of hierarchical task network (HTN) planning to capture high-level intentions. We also present two ongoing directions: extending our logical framework with hierarchical decomposition and revision of intentions based on instrumentality. 1 Background and Motivations The mental attitudes of belief, desire, and intention play a central role in the design and implementation of autonomous agents. In 1987 [Bratman] proposed their integration into a belief-desire-intention (BDI) theory that was seminal in AI. Since then numerous approaches were built on the BDI paradigm, both practical (BDI architectures and BDI agents) and formal (BDI logics). The logical approaches that were the most influential are due to [Cohen and Levesque, 1990] and to [Rao and Georgeff, 1991]. However, the practical and logical approaches evolved separately and neither was fruitful for the other. Bratman highlighted the fundamental role of an agent’s future-directed intentions: they are high-level plans to which the agent is committed. Such high-level plans cannot be executed directly: they have to be refined, resulting in more and more elaborate plans. Taking the example of going to Melbourne, Figure 1 shows the process of refinement. The lower-level intentions that are inserted are instrumental for the high-level intention they refine [Bratman, 2009]. At the end of the refinement process plans only contain basic actions: actions the agent can perform intentionally. The operations of refinement of intentions are fundamental in the BDI model. As pointed out in [Rao and Georgeff, 1991], “the potential of non-primitive events for decomposition into primitive events can be used to model hierarchical plan development”. However, the instrumentality relation between higher-level and lower-level intentions is not accounted for in the existing BDI logics, including Cohen&Leveques’s and Rao&Georgeff’s BDI theories and those inspired by their theories, where intentions are viewed as a basic attitude and in Figure 1: (a) The initial intention of the agent is to go to Melbourne; (b) the initial intention is refined by a lower-level intention to go to Melbourne by plane; (c) the intention to fly to Melbourne is further refined into two intentions: to go to the airport and to take the plane. consequence there is no appropriate account of intention refinement. The aim of this research project is to provide a logical analysis of this hierarchical refinement process.