問100
頻出度★★★
レコードの関連付けに関する説明のうち，関係データベースとして適切なものはどれか。
平成30年度 秋期 ITパスポート試験 問100
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 100
Incorrectア
Associating records by the same row position counted from the top of each table is incorrect. Records in a relational database have no notion of order (row position), and the associations are preserved even if the ordering changes. Matching by position is not part of the relational-model way of thinking.
- イ
正解 In a relational database, records in one table are associated with records in another through the values of corresponding fields. Specifically, the value of a primary key in one table is held as the same value by a foreign key in the other table, which indicates that the two records point to the same entity. The association does not depend on row position or physical pointers; it is determined solely by whether the values themselves match. This is the characteristic of the relational model, and choice イ describes it correctly.
Incorrectウ
Linking records by pointers that represent parent-child relationships is the approach of a hierarchical database (or a network database), not a description of a relational database. The relational model associates records by values, not by pointers.
Incorrectエ
A hash function is a technique used to determine the storage location of data or to speed up searches (implementing indexes); it is not a mechanism for logically associating records. The basis of association is matching values, not a hash function.
ここがポイント
- A relational database associates records through the values of corresponding fields (matching primary key and foreign key); it does not depend on row position or pointers.
- Hierarchical and network databases represent parent-child relationships with pointers, which is the difference from the relational model.
用語