During the last few years, and in an attempt to provide an ecient alternative to classical methods to designing robot control structures, the behavior-based approach has emerged. Its success has largely been a result of the bottom-up development of a number of fast, tightly coupled control processes. These are specically designed for a particular agent-environment situation. This new approach, however, has some important limitations because of its lack of goaldirectedness (it provides no guarantee to fulll the goal) and
exibility (the control is entirely wired and the robot is limited to the behaviors implemented by its designer). In earlier work we presented a model for an architecture that would deal with some of these problems. The architecture bases on two levels of arbitration, a local level which enables the robot to \live" in a particular real world situation, and a global level which ensures that the robot reactions be consistent with the required goal. In this paper ...