Robust active super tier systems

This paper proposes a framework for designing tier systems. First we suggest to implement robust tier automata for each tier T/sub i/ implemented by the processors that the tier consists. The robust tier automata is a useful abstraction that allows the distribution of the tasks of a tier (and its stubs) in a way that ensures availability, consistency, and recovery in the presence of faults. Then we suggest the active tier framework where the computation of a user request is progressing in several paths in the tier system which may intersect, leaving footprints for each other. At last we propose the super tier architecture, which correlates equivalent tiers in order to gain more robustness and load balancing. We present and analyze optimistic, pessimistic and semi-optimistic approaches for computing over the active tier system with super tiers.