Whenever a problem is observed, we want to record its key elements, so that we can then investigate causes and cures. In particular, we want to know the following:
- Location: where did the problem occur?
- Timing: when did it occur?
- Symptom: what was observed?
- End result: which consequences resulted?
- Mechanism: how did it occur?
- Cause: why did it occur?
- Severity: how much was the user affected?
- Cost: how much did it cost?
- Count: optional
A failure report addresses each of the eight attributes as listed above:Failure report
Location: such as installation where failure was observed
Timing: CPU time, clock time etc.
Symptom: type of error message or other indication
End result: description of failure, like "wrong output"
Mechanism: chain of events leading to failure
Cause: reference to possible fault(s) leading to failure
Severity: reference to a well defined scale, "critical",...
Cost: cost to fix plus cost of lost potential businessIn the book there is listed sets of values for each of these attributes:
for "end result": operating system crash, application program aborted, service degraded, loss of data, wrong output, and no output,
for "severity": catastrophic, critical, significant, and minor.For an example, see Example 5.4.