問34
頻出度★★★
ソフトウェアの品質特性は, 機能性, 使用性, 信頼性, 移植性などに分けられる。使用性に分類されるものはどれか。
平成23年度 秋期 ITパスポート試験 問34
マネジメント系システム開発技術 › システム開発技術
This question's explanation and your answers so far.
解説
問 34
Incorrectア
“It provides execution results and operations as specified in the specification document” describes whether the required functions match the specification and are correctly implemented, so it is classified as functionality. Functionality consists of suitability (whether the necessary functions are provided), accuracy (whether correct results are obtained), interoperability (whether the software can work together with other systems), security or confidentiality (whether it is protected from unauthorized access), and so on. Matching the specification is a different viewpoint from being easy to use, so it does not fall under usability.
Incorrectイ
“The software has a long mean time between failures” is classified as reliability. Mean time between failures (MTBF) is an indicator that expresses the average operating time from one failure to the next; the larger the value, the less prone to failure the software is and the more stably it keeps running. Reliability consists of maturity (how unlikely faults are to occur), fault tolerance (whether functions can be maintained even when a fault occurs), recoverability (whether it can recover from a fault), and so on. Being unlikely to fail has nothing to do with how easily users can remember the operations, so this is not usability.
Incorrectウ
“It can also run on other OS environments” is classified as portability. Portability is the quality characteristic that expresses how easily software can be moved to and run in a different environment such as other hardware, an operating system, or middleware, and it includes adaptability, ease of installation (installability), the ability to be swapped in for another product (replaceability), and so on. Being able to run in different environments shows flexibility for the development and operations side; it does not show whether users can learn the operations easily, so it does not amount to usability.
- エ
正解 The correct answer is エ. Usability is the quality characteristic that expresses whether software is easy to understand, easy to remember, and easy to use for its users. In ISO/IEC 9126 (now carried on by JIS X 25010 / ISO/IEC 25010), the sub-characteristics of usability include understandability, which is about being easy to grasp; learnability, which is about being easy to remember and learn; and operability, which is about how easy the actual operations are. Choice エ, “the time it takes for users to become proficient is short”, means that the learning time a user needs before being able to handle the software well is short — in other words, the operations are easy to remember — and that is exactly learnability. A product that lets you guess how to operate it just by looking at the screen without reading through the manual, and that lets you do the work you want after only a little practice, is rated as having high usability. What deserves attention here is that usability is a viewpoint independent of whether the functions work correctly. Even if the software runs accurately just as the specification document says, if the screens are hard to understand, the operating steps are complicated, and it takes several days to master, usability is judged to be low. Conversely, the reason quality is evaluated by dividing it into different viewpoints such as functionality, reliability, usability, and portability is precisely to keep this kind of user-side quality from being hidden behind functions and performance and overlooked. Therefore, the item classified as usability is エ.
ここがポイント
- The classification of software quality characteristics (ISO/IEC 9126, currently JIS X 25010) — six characteristics: functionality (does it provide the specified functions correctly), reliability (does it keep running without failing), usability (is it easy to understand and easy to use), efficiency (does it avoid wasting resources and time), maintainability (is it easy to fix and improve), and portability (is it easy to move to another environment). The way to solve the question is to sort the choices by which viewpoint each one describes.
- Sub-characteristics of usability — understandability (easy to grasp), learnability (easy to remember, short time needed to become proficient), operability (easy to operate), and so on; they refer to ease of use as seen from the user side. Remember wordings such as “the time it takes to become proficient is short” or “it can be operated without a manual” as keywords for usability. Do not confuse them with MTBF (mean time between failures), which is an indicator of reliability.
用語