問5
頻出度★★★
DFD の記述例として, 適切なものはどれか。
平成30年度 春期 ITパスポート試験 問5
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 5
Incorrectア
The figure shows state 1 and state 2 changing back and forth triggered by event A, event B, event C, and event D; this is a state transition diagram. It represents changes in the state of a system or object, not a DFD that represents the flow of data.
- イ
正解 The correct answer is イ. A DFD (Data Flow Diagram) represents a business or system by focusing on how data flows through it, and it is made up of four elements: processes (circles/bubbles), data flows (arrows), data stores (parallel lines or open rectangles = where data is kept), and external entities (boxes = the source and destination of data). In figure イ, the two circles process 1 and process 2 (processes) are connected in order by the arrows data A -> data B -> data C (data flows), and data file 1 (a data store drawn as parallel lines) is connected to process 1. This follows the standard DFD notation exactly, so it is an appropriate example.
Incorrectウ
The figure connects entity 1 and entity 2 with a relationship (diamond) and shows a one-to-N correspondence (multiplicity). This is an E-R diagram (entity-relationship diagram), which represents the structure of data and the relationships between entities, not a DFD that represents the flow of data.
Incorrectエ
The figure uses a decision (diamond) to test a condition and, depending on the result, branches to process 1 or process 2. This is a flowchart, which represents the steps of processing and the flow of control (sequence, branching, repetition), not a DFD that represents the flow of the data itself.
ここがポイント
- A DFD (data flow diagram) is a diagram that focuses on the flow of data, made up of four elements: processes (circles), data flows (arrows), data stores (parallel lines), and external entities (boxes).
- Telling it apart from similar diagrams: a state transition diagram = changes in state, an E-R diagram = relationships between entities (data structure), a flowchart = processing steps and control flow. Distinguish them by what each diagram focuses on.
用語