COLLABORATIVE PLANS FOR COMPLEX GROUP ACTION

The original formulation of SharedPlans by B. Grosz and C. Sidner (199 0) was developed to provide a model of collaborative planning in which it was not necessary for one agent to have intentions-to toward an ac t of a different agent. Unlike other contemporaneous approaches (J.R. Searle, 1990), this formulation provided for two agents to coordinate their activities without introducing any notion of irreducible joint i ntentions. However, it only treated activities that directly decompose d into single-agent actions, did not address the need for agents to co mmit to their joint activity, and did not adequately deal with agents having only partial knowledge of the way in which to perform an action . This paper provides a revised and expanded version of SharedPlans th at addresses these shortcomings. It also reformulates Pollack's (1990) definition of individual plans to handle cases in which a single agen t has only partial knowledge; this reformulation meshes with the defin ition of SharedPlans. The new definitions also allow for contracting o ut certain actions. The formalization that results has the features re quired by Bratman's (1992) account of shared cooperative activity and is more general than alternative accounts (H. Levesque et al., 1990; E . Sonenberg et al., 1992).