問67
頻出度★★★
フールプルーフの考え方として, 適切なものはどれか。
平成21年度 秋期 ITパスポート試験 問67
テクノロジ系システム構成要素 › システムの評価指標
This question's explanation and your answers so far.
解説
問 67
Incorrectア
Keeping damage to a minimum when a fault occurs and bringing the system into a safe state describes fail-safe design. It is the idea of falling to the safe side (stopping, cutting off, and so on) when a failure happens; its starting point is equipment failure, so it differs from fool-proof design, which prevents human operating mistakes. Examples: a traffic light that automatically turns red during a power outage, and a kerosene heater that puts itself out when it tips over.
Incorrectイ
Assuming that failures are bound to occur and keeping their impact to a minimum through means such as device redundancy describes fault tolerance. It is the idea of continuing processing even when a failure occurs, by using redundant configurations; it is not a countermeasure against operating mistakes. Examples: duplicated power supplies and disks, and cluster configurations.
Incorrectウ
Driving the probability of a failure as close to zero as possible describes fault avoidance (designing for high reliability), which keeps failures from happening in the first place through high-quality parts and thorough testing. It is about lowering the failure rate, so its purpose differs from fool-proof design, which renders human operating errors harmless.
- エ
正解 Fool-proof design starts from the premise that people will inevitably make mistakes, and builds in mechanisms beforehand so that even when a user operates the system incorrectly, it does not lead to a dangerous state or a malfunction. Choice エ says exactly that: even if a person makes a mistake when operating the system, it preserves the system's safety and reliability, which matches this definition. The deciding point is whether the cause is a human operating mistake: only fool-proof design takes human error, rather than equipment failure, as its starting point. Familiar examples include a washing machine or microwave oven that will not run unless the door is closed, an input check that will not let you type letters into a numeric field, and a confirmation dialog before deletion.
ここがポイント
- Fool-proof: assuming people will make operating mistakes, design things so that even a wrong operation does not lead to danger or malfunction (the cause is human error).
- Sorting out the reliability-design terms that are easy to confuse: fail-safe (fall to the safe side when a failure occurs) / fault tolerant (redundancy keeps it running despite a failure) / fault avoidance (lower the probability of failure itself). Tell them apart by asking whether the cause is a person or the equipment, and what happens after a failure.
用語