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Patterns for Fault Tolerant Software by Robert S. Hanmer

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Chapter 8. Fault Treatment Patterns

After an error is processed, fault treatment prevents the error from reoccurring. This includes repairing the fault. This can mean patching the system, which is installing a new fault-free version of the software or the data. It can also mean correcting a procedure so that a person won't cause the same error again.

Sometimes error detection will immediately precede fault treatment without the execution of an error recovery phase.

The steps of fault removal are: verification, diagnosis and correction. Verification is done to determine if the system behavior conforms to its specifications. This is done to check whether the fault is still present in the system. The aim of diagnosis is to determine the cause, both in terms of location of the fault and the nature of the fault. Correction is the step in which the fault is made passive. After correction, verification is needed again to see that the system behavior is restored to conformance with its specification. Fault removal is an example of corrective maintenance.

Not all maintenance tasks are corrective. Preventive maintenance corrects a fault before it is activated. Routine Audits (24), in Chapter 5, is an example of something that is both an error detection technique and a preventive maintenance task.

Table 8.1. Fault treatment patterns

Pattern

Pattern intent

Verification, diagnosis, correction

Let Sleeping Dogs Lie (58)

Consider the true benefits to the system of correcting the faults versus leaving the ...

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