問39
頻出度★★★
ITサービスにおいて, 合意したサービス時間中に実際にサービスをどれくらい利用できるかを表す用語はどれか。
平成21年度 春期 ITパスポート試験 問39
テクノロジ系セキュリティ › 情報セキュリティ管理
This question's explanation and your answers so far.
解説
問 39
Incorrectア
Responsiveness is the property concerning how quickly a result comes back after a request is issued (response time). It is a performance measure of whether a service is fast, not a term for the proportion of time the service was actually usable within the agreed hours. Even if responses are slow, availability is maintained as long as the service itself keeps running, which shows that they are different concepts.
- イ
正解 The correct answer is イ, availability. Availability means the degree to which a system or service can be used when it is needed; in IT services it is measured by how much of the agreed service hours set in the SLA (service level agreement) the service was actually usable. The wording in the question, “how much a service can actually be used during the agreed service hours”, matches this definition exactly. Concretely it is expressed by measures such as an availability rate (for example 99.9%), or availability rate = MTBF ÷ (MTBF + MTTR) using the mean time between failures (MTBF) and the mean time to repair (MTTR); the fewer failures and outages there are, the higher the availability. Redundancy (duplication), backups and cluster configurations are typical means of raising availability.
Incorrectウ
Integrity is the property that information is not destroyed, tampered with or missing, and is kept accurate and complete. It is one of the three elements of information security, but what it deals with is the correctness of data, not the length of time a service can be used.
Incorrectエ
Confidentiality is the property that only authorized people can access information and that it does not leak to anyone else. It is likewise one of the three elements of information security, but it is a concept about controlling access rights and has nothing to do with how much a service can be used.
ここがポイント
- Availability = the degree to which something can be used when you want to use it. In IT services it is expressed as the ratio of the actually usable time to the agreed service hours (the availability rate), calculated as availability rate = MTBF ÷ (MTBF + MTTR).
- The three elements of information security (CIA) are distinguished as follows: confidentiality = only authorized people can view it; integrity = the information is accurate and has not been tampered with; availability = it can be used when needed. Responsiveness is not one of the three elements but a performance term for the speed of processing.
用語