Moreover, it makes the plan rather rigid. There is no provision for going back to the planning level if the reactive level encounters an unexpected difficulty. Consider the communication between the logical planner and the reactive executor of steps. The following considerations apply. When the goal is achieved, the observation program takes another look at the scene and modifies the logical database accordingly.
Inference then resumes.
Any information needed to achieve a goal that cannot be obtained by the achiever directly from the scene must be provided to the goal-achiever in advance. This scheme provides for no other communication between the logic part of the system and the reactive part and is therefore less sophisticated than many existing systems that plan and execute. At least conceptually, however, it seems appropriate to begin with this primitive interaction and then study what more this particular fruit fly may require.