Exceptions and Contingencies Handling in a SCADA System
The use of rollback is a fundamental flaw in some existing distributed control systems because the advance in time and in external world situations means that what had been a correct state in the past may no longer be a correct state in real time and distributed systems. In such systems rollback is not restoring to a state that is consistent with the current external environment. Forward error recovery provides a potential solution to such a situation to handle exception rather than backward recovery. A contingency is an unusual but anticipated situation for which the normal flow of instructions would not produce the appropriate results that should be expected. We will discuss how to handle contingencies and exceptions in a SCADA (Supervisory Control and Data Acquisition) system using resumption and termination models of exception handling.