問38
頻出度★★★
システム開発プロセスを, 要件定義, 外部設計, 内部設計の順番で実施するとき, 内部設計で行う作業として, 適切なものはどれか。
平成24年度 秋期 ITパスポート試験 問38
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 38
Incorrectア
Setting the target value for screen response time is a task performed during requirements definition. Targets concerning performance and quality — response time, availability rate, number of transactions processed — are called non-functional requirements, and they are the users' own demands about what the system must provide and at what level. If the target values are not fixed during requirements definition, the later external design and internal design stages cannot judge what has to be satisfied. Internal design is the process of working out the means to achieve targets that have already been decided, not the process of deciding the target values themselves, so this is incorrect.
Incorrectイ
Dividing the system into subsystems is a task performed during external design (basic design). Just as a sales management system is divided into business units such as order taking, inventory, and billing, deciding what units make up the system as a whole is a design of the overall structure that follows the divisions of the users' business, and it must be settled before moving on to internal design. Internal design is the process of further detailing the inside of each subsystem that has been divided in this way, so the division itself is a task of the preceding process, and this is incorrect.
- ウ
正解 The correct answer is ウ. System development proceeds in the order requirements definition (deciding what users want) → external design (deciding the outside that users can see) → internal design (deciding the inside that developers see) → programming, refining step by step from the outside inward. Internal design is the process of translating the specifications fixed in external design into the internal structure that will actually run on a computer, and its distinguishing feature is that it deals with the parts users cannot see. Choice ウ, “determine the length and attributes of the records stored in the database”, is exactly this kind of decision about internal structure. At the external design stage, only logical data items are decided, such as “handle the customer name” or “handle the order date”; how those items are actually held in the implementation — attributes such as whether they are a character type or a numeric type, and the number of digits and the record length that say how many bytes can be stored — belongs to implementation circumstances on the computer side, not to the users' business requirements. Deciding these is physical data design, and that is a task performed in internal design. Therefore ウ is appropriate.
Incorrectエ
Designing the layout of input/output screens and reports is a task performed during external design. Screens and reports are the interface that users operate and see directly, and their content has to be confirmed and agreed on together with the users, so they belong to external design, which decides the outside. What internal design handles is the parts users cannot see, such as the structure of the programs running behind that screen and the way data is held. Distinguishing the visible parts from the invisible parts is the key point of this question, and エ is on the visible side, so it is incorrect.
ここがポイント
- Remember that the design processes advance “from the outside inward”. Requirements definition = what to build (business requirements and the target values of non-functional requirements); external design (basic design) = the outside that users can see (subsystem division, screen and report layouts, logical data design); internal design = the inside that developers see (program division, module structure, physical data design). When a judgment is hard to make, just ask “is this visible to the user?”
- Data design is split between logical and physical across two different processes. Logical data design, which decides what data items are needed, belongs to external design; physical data design, which decides how those items are held in the implementation (data type, number of digits, record length, file organization), belongs to internal design.
用語