問11
頻出度★★★
あるレストランでは, 受付時に来店した客の名前を来店客リストに記入し, 座席案内時に来店客リストと空席状況の両方を参照している。この一連の業務を DFD で表現したものとして, 最も適切なものはどれか。
令和2年度 ITパスポート試験 問11
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 11
Incorrectア
The arrow directions are reversed. “Visitor list → reception” is the direction in which reception reads out the visitor list, but in the operations reception writes (records) into the visitor list, so the correct flow reception → visitor list is reversed. Also, “seating guidance → vacancy status” is the direction in which seating guidance writes to the vacancy status, but in the operations seating guidance references (reads) the vacancy status, so the correct flow is vacancy status → seating guidance, which is likewise reversed. It also includes reception → seating guidance, which does not exist in the operations, so it is inappropriate.
Incorrectイ
The arrow entering the vacancy status is “reception → vacancy status”, the direction in which reception writes to the vacancy status; but it is seating guidance that references the vacancy status, so it should be vacancy status → seating guidance — the direction is wrong. It also includes “seating guidance → reception”, which does not exist in the operations, and it lacks the flow in which reception records into the visitor list (reception → visitor list). Only “visitor list → seating guidance” is correct, so as a whole it is inappropriate.
Incorrectウ
All three arrows originate from reception. Only “reception → visitor list”, the recording (write), is correct; but “reception → vacancy status” is the direction in which reception writes to the vacancy status, which is opposite to the operations (it is seating guidance that references it). Furthermore, the only arrow entering seating guidance is “reception → seating guidance”, so the flows in which seating guidance references both the visitor list and the vacancy status (visitor list → seating guidance, vacancy status → seating guidance) are not represented, making it inappropriate.
- エ
正解 In a DFD, the circles labeled “reception” and “seating guidance” represent processes, while the parallel lines labeled “visitor list” and “vacancy status” represent data stores (accumulated data); the arrows show the direction in which data flows. Breaking down the operations in the question: (1) at reception the customer's name is written into the visitor list = reception → visitor list; (2) at seating guidance the visitor list is referenced = visitor list → seating guidance; (3) likewise the vacancy status is referenced = vacancy status → seating guidance. Option エ shows exactly these three flows (reception → visitor list, vacancy status → seating guidance, visitor list → seating guidance) in the correct directions, and the directions of writing and reading both match the operations, so it is the most appropriate.
ここがポイント
- The four elements of a DFD: process (circle), data store (parallel lines = accumulation of data), data flow (arrow = the direction in which data flows), and external entity (source/sink). The “direction” of an arrow means the direction in which data moves.
- Determine the direction from the operation: recording (writing) goes process → data store, while referencing (reading) goes data store → process.
用語