問91
頻出度★★★
E-R図で表現するものはどれか。
平成31年度 春期 ITパスポート試験 問91
テクノロジ系データベース › データベース設計
This question's explanation and your answers so far.
解説
問 91
Incorrectア
“The physical placement of data within an HDD” concerns how data is stored on a storage device, which is a physical-implementation-level matter. An E-R diagram represents the semantic structure of data (the conceptual data model) and does not represent the physical location where data is placed.
- イ
正解 An E-R diagram (Entity-Relationship diagram) is a notation used in database design that depicts the objects being handled as “entities” and the connections between those entities as “relationships”. For example, you connect the two entities “customer” and “order” with a line to express a correspondence such as “one customer has many orders” (e.g., one-to-many). In other words, what an E-R diagram represents is precisely “the relationships among entities”, so choice イ is correct.
Incorrectウ
It is flowcharts or DFDs (data flow diagrams) that represent “the flow of processing”. An E-R diagram represents the static relationships among data and does not deal with the order in which processing flows.
Incorrectエ
Representing the handoff of data by focusing on “input data and output data” is the role of DFDs (data flow diagrams) and the like. An E-R diagram focuses on entities and relationships and does not take input/output data itself as what it represents.
ここがポイント
- An E-R diagram is a conceptual-design notation that models data structure using entities and relationships.
- Do not confuse diagrams that serve different purposes: the flow of processing is shown by flowcharts/DFDs, while physical placement belongs to physical design.
用語