問47
頻出度★★★
システム開発の外部設計において行う作業はどれか。
平成21年度 春期 ITパスポート試験 問47
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 47
- ア
正解 The correct answer is ア. External design is the phase that decides how the system looks and how it can be used when seen from the outside, so it designs the parts that users come into contact with and can see. Concretely, its targets include screen layouts and input fields, the layout of reports (printed forms), the coding scheme (such as the number of digits and the way employee numbers or product codes are assigned), and logical data design. Screen and report layouts are exactly what users operate and look at directly, so they are a typical task of external design. The trick for judging is to divide things by “is it visible to users, or visible only to developers”: if it is visible it belongs to external design, and if it is not visible it belongs to internal design and the phases after it.
Incorrectイ
Finalizing performance requirements (response time, the number of items processed, and so on) is work in requirements definition, which comes before external design. In requirements definition you agree with the users on “what is required of the system”, and external design then takes those requirements and works out “how it will be shown to users”. Design cannot start before the requirements are fixed, so in terms of phase order this is not external design.
Incorrectウ
Design of physical data (the actual file organization, how tables are stored, how indexes are held, and so on) is work done in internal design. The data design handled in external design goes only as far as logical data design, which organizes the data items and their relationships as seen by users; how they are realized on the storage device is an internal matter that users cannot see.
Incorrectエ
Design of the programs is work in program design (detailed design), which is carried out after internal design. It is the stage where the division into modules and the processing steps inside each module are decided, the innermost design aimed at programmers. Both its phase and its viewpoint differ from external design, which decides the specifications visible to users.
ここがポイント
- In the waterfall model the phases run in the order requirements definition → external design → internal design → program design → programming → testing. For a question about phases, first recall this order and then match the task in the question to one of the phases.
- External design = the parts visible to users (screen and report layouts, code design, logical data design); internal design = the internal structure seen from the developer side (physical data design, division into functions). “Whether users can see it” is the criterion that separates the two.
用語