If this method fails, the allocation problem is solved through more elaborate resource management that also modifies the abstract plan. The planning phase can suggest intent of desirable modifications to the scheduling phase in the form of following resource allocation policies: (1) Must maintain concurrency of the plan. (2) Allow serialization of the concurrent plan by moving actions from one step (level) to another less-constrained step. (3) Allow introduction of actions to free unnecessary allocations and re-allocate the freed resources when needed again.