問2
頻出度★★★
業務プロセスのモデリングに用いられる DFD の記述例として，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2
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 2
Incorrectア
This figure connects circles (nodes) into a network with arrows (activities); it is an arrow diagram (PERT chart). It is a scheduling notation used to derive the overall schedule and the critical path from the precedence relations among activities and their durations, and its arrows represent activities, not the flow of data. Nowhere does it contain the data store (two parallel lines) that is the decisive mark of a DFD.
- イ
正解 The correct answer is イ. A DFD (Data Flow Diagram) is a structured-analysis notation that describes business operations from the viewpoint of “where data comes from, which processes it passes through, where it is stored, and where it goes out.” Its symbols are limited to the following 4: (1) process = a circle or a rounded rectangle, (2) data store (where data is accumulated) = two parallel lines, (3) data flow (the movement of data) = an arrow, and (4) source and sink (external entity) = a rectangle. In the figure of イ, two circles (processes) are connected by arrows (data flows), and each exchanges arrows with the two parallel lines (data stores) above and below it. Because the symbols unique to a DFD — process, data store, and data flow — are all present, this is an appropriate example of a DFD.
Incorrectウ
This figure is a tree structure in which rectangles branch downward from a top node; it corresponds to an organization chart, a WBS (work breakdown structure), or a hierarchical structure diagram (such as the visual table of contents of HIPO). It shows the composition and hierarchy obtained by breaking a whole down step by step, and expresses neither the flow of data nor where data is stored, so it is not a DFD.
Incorrectエ
This figure looks like a fish skeleton, with slanted branches stuck into a single horizontal arrow (the backbone); it is a cause-and-effect diagram (fishbone diagram, one of the seven QC tools). It is used to organize and list the factors that cause a given result (characteristic) into major and minor branches, and it is not a notation for showing the flow of data in a business process.
ここがポイント
- Memorize the notation of a DFD and its 4 components: process (circle), data store (two parallel lines), data flow (arrow), and source and sink = external entity (rectangle). When telling notations apart, the surest way is to judge by “the symbol that appears only in that notation”; for a DFD, the two parallel lines of the data store are the mark.
- Sort out the roles of the notations that are easily confused with a DFD: an arrow diagram = scheduling and the critical path; a hierarchical structure diagram or WBS = breaking down work or an organization; a cause-and-effect diagram = analyzing the factors behind a result; an E-R diagram = relationships among data (entities). Only the DFD is a business-process modeling technique that focuses on the flow of data.
用語