問87
頻出度★★★
売上伝票のデータを関係データベースの表で管理することを考える。 売上伝票の表を設計するときに, 表を構成するフィールドの関連性を分析し, データの重複及び不整合が発生しないように, 複数の表に分ける作業はどれか。
令和元年度 秋期 ITパスポート試験 問87
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 87
Incorrectア
'Join' is a relational operation that links multiple tables into one using a common field as the key to retrieve data — the opposite of the design task of splitting a table. It is not the table splitting done to prevent duplication and inconsistency, so it is wrong.
Incorrectイ
'Projection' is a relational operation (a data-retrieval operation) that extracts only the needed columns (fields) from a table. It is not the work of designing or splitting a table's structure, so it is wrong.
- ウ
正解 The correct answer is ウ 'Normalization'. Normalization is a design task that analyzes the relationships among fields (functional dependencies) and splits items mixed together in a single table into multiple tables, grouping them by meaning. If you cram fields such as slip number, date, customer name, product name, unit price, and quantity into one table like a sales slip, the same customer name or product unit price gets recorded over and over (duplication), and fixing only one of them makes the values disagree (inconsistency). By splitting into a customer table, a product table, a sales-detail table, and so on through normalization, each piece of data is managed in only one place, which prevents duplication and inconsistency. This matches the task described in the question — analyzing relationships and splitting into multiple tables so that duplication and inconsistency do not occur — so ウ is correct.
Incorrectエ
'Exclusive control' is a concurrency control mechanism that uses locks and similar means to prevent conflicts when multiple users try to update the same data at the same time. It relates to maintaining data consistency, but it is not the task of splitting fields at the table design stage, so it is wrong.
ここがポイント
- Definition of normalization: a design task that analyzes the relationships among fields (functional dependencies) and splits a table into multiple tables to eliminate data duplication and inconsistency.
- Be able to distinguish relational operations (join = combining tables, projection = extracting columns) and concurrency control (exclusive control) from normalization, which is a table-structure design task.
用語