問83
頻出度★★★
関係データベースの構築を次の a～c の工程で行うとき, 実行順序として適切なものはどれか。 a 管理するデータ項目の洗い出し b 対象業務の分析 c 表の作成
平成26年度 春期 ITパスポート試験 問83
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 83
Incorrectア
In a→b→c, you would identify the data items to be managed before analyzing the business. If you decide which items are needed while the target business operations are still unknown, items that the actual operations require may be missed, or unused items may be built in. Business analysis (b) is the process that supplies the information on which identifying data items (a) depends, so b must come before a.
- イ
正解 The correct answer is イ, b→a→c. Building a relational database proceeds in order from the upstream process of understanding the business to the downstream process of actually creating tables. First comes b, analyzing the target business operations. Unless you know what the operations are, what information arises from them, and who uses it and how, you cannot decide what should go into the database at all. Next comes a, identifying the data items to be managed. Based on the results of the business analysis, you identify the data items that must be managed, such as customer name, product code, and order date, and you organize the relationships among those items (using an E-R diagram, for example). Last comes c, creating tables. Based on the identified items, you decide the table name, the column (data item) structure, the data types, the primary key, and so on, and actually define the tables. In other words, the order is: understand the business, decide what to hold, then build the container. Therefore b→a→c is appropriate.
Incorrectウ
In b→c→a, you would create tables right after analyzing the business, without having decided the data items. To create a table, the columns (data items) it will hold must already be fixed, so tables (c) cannot be created while identifying the items (a) is not yet finished. The order of a and c is reversed.
Incorrectエ
In c→a→b the order is completely reversed, meaning you would start from creating tables, the most downstream step. With neither the business analysis nor the identification of data items done, there is no way to decide the column structure of the tables, and after building them you would discover missing or excess items and have to rebuild. This is the typical mistake of starting implementation without going through design.
ここがポイント
- The basic flow of database design is: analyze the target business operations, identify the data items to be managed (conceptual design, E-R diagram), then create the tables, moving from the upstream analysis and design processes to the downstream implementation process. Because the output of an upstream step is the input to the next one, the order cannot be swapped.
- In a relational database, data is managed in tables made up of rows and columns. Columns correspond to the data items to be managed, so keep this dependency in mind: if the items are not fixed, the table cannot be defined.
用語