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A role, r, consists of a specification of an agent's internal and external behaviors. The conditions and arguments of any behavior can depend on the agent's current role, which is a function of its internal state. At the extreme, a top-level external behavior could be a switch, calling an entirely different behavior sub-graph for each possible role. However, the role can affect the agent's overall behavior at any level of its behavior graph: it could affect just the arguments of a behavior deeply embedded in the behavior graph.

Roles may be rigid, completely specifying an agent's behavior. Or they may be flexible, leaving a certain degree of autonomy to the agent filling the role. For example, consider an agent that has access to a clock and that can blow a whistle. Role r could rigidly specify that the agent filling it must blow a whistle on the hour every hour. On the other hand, role r could leave some flexibility to the agent that fills it, specifying that no fewer than 25% but no more than 75% of the times that the hour changes, the agent must blow a whistle. In this case, the agent must stay within a parametric range in order to successfully fill the role, but on every given hour change, it can choose for itself what to do. By specifying ranges of parameters or behavior options, the agent filling role r can be given an arbitrary amount of flexibility.

A role in the robotic soccer domain, can be a position such as a midfielder. In the hospital maintenance domain, a role could specify the wing of the hospital whose floors the appropriate agent should keep clean, while in the web search domain, it could specify a server to search.

Peter Stone
Thu Dec 17 15:26:44 EST 1998