問14
頻出度★★★
業務プロセスの分析時に作成する DFD の説明として, 適切なものはどれか。
平成22年度 春期 ITパスポート試験 問14
ストラテジ系システム戦略 › 業務プロセス
This question's explanation and your answers so far.
解説
問 14
Incorrectア
Saying that it “shows the various kinds of data handled in the business and the mutual relationships among them” describes an E-R Diagram (Entity Relationship Diagram). An E-R diagram treats data as entities and expresses the relationships between entities (one-to-one, one-to-many, many-to-many, and so on), which leads on to database design; its focus is the static relationships among data items. What a DFD shows is data moving dynamically between processes, not relationships among data items, so this is wrong.
Incorrectイ
Showing data “hierarchically detailed from sets down to elements” describes a data structure diagram (a diagram that shows the hierarchical structure of data items), which breaks the structure of data down step by step. Its subject is strictly the internal structure of data; it does not express how processes connect to one another or how data is handed over between them. The main focus of a DFD is processes and data flows, so this is wrong.
- ウ
正解 The correct answer is ウ. A DFD (Data Flow Diagram) is an analysis technique that views a business as a collection of “processes” and diagrams what data flows from one process to another. It has four building blocks: the “process”, which transforms data; the “data flow” (an arrow), which represents data moving; the “data store”, which represents where data is kept; and the “external entity” (source and sink), which represents where data originates outside the business and where it goes. Connecting these with lines makes the flow of data through the whole business visible. Therefore choice ウ, which says it shows the processes that make up the business and the flow of data passed between them, is an appropriate description of a DFD. A DFD is used in business process analysis (understanding the current business or designing a new one) so that stakeholders can share an understanding of where each piece of data is created, where it is passed to, and where it is stored.
Incorrectエ
Showing “the content of the processes hierarchically from overview to detail” describes diagrams that break functions down from higher levels to lower ones, such as HIPO or a function hierarchy diagram (hierarchy chart). It merely arranges processes in layers; it does not show what data flows between one process and another. A DFD can also be used in a layered, progressively detailed way, but as a statement of what a DFD essentially is, エ is inappropriate because it never touches on the flow of data, and ウ, which states that point explicitly, is the correct one.
ここがポイント
- A DFD (Data Flow Diagram) is a diagram that visualizes the processes making up a business and the flow of data passed between those processes. It has four building blocks: process, data flow, data store, and external entity (source and sink).
- Tell the diagrams used in analysis apart: relationships among data are drawn with an E-R diagram, progressive detailing of the internal structure of data with a data structure diagram, and breaking functions down from overview to detail with HIPO or a function hierarchy diagram. The keywords that identify a DFD are the combination of “processes” and “flow of data”.
用語