| form of fault-tolerant software design in which several diverse modules are invoked in sequence to perform a given task until one of them is successful
Note 1 to entry: Each of the modules is capable of performing the given task, but in a different way. ‘Success’ is judged by the fact that the output satisfies an acceptance test performed by an adjudicator. A module in the sequence is invoked only if all earlier modules fail.
Note 2 to entry: If a module fails then backward error recovery is performed before invoking the next module.
Note 3 to entry: The recovery block scheme is an example of standby redundancy.