問63
頻出度★★★
関係データベースを構築するに当たり, データの正規化を行う目的はどれか。
平成22年度 秋期 ITパスポート試験 問63
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 63
Incorrectア
A checksum is an error-detection technique in which a check value computed from the data by some rule is attached to it, and is later recomputed and compared to see whether the two match, so that corruption or tampering is detected. It is a mechanism for confirming that data has not been damaged, and both its purpose and its means differ from normalization, which organizes table structure and removes duplication.
- イ
正解 The correct answer is イ. Normalization is the work, done when designing a relational database, of splitting the items packed into a single table into separate tables by relationship, thereby removing the state in which the same fact is held redundantly in many places (data redundancy). For example, if an order table also records the customer name and address, the same customer appears again on many rows, once for every order. If that customer's address then changes, every one of those rows must be corrected, and any row that is missed leaves the contradiction of one and the same customer having different addresses (an update anomaly). Once normalization separates out a customer table and the order table holds only the customer code, correcting the address means changing just one row of the customer table, and no contradiction arises. In other words, eliminating redundancy leads to easier changes and to keeping the data consistent, that is, to improved maintainability. イ, which states this cause and effect, is correct.
Incorrectウ
Unifying the character encoding (the character set and the encoding scheme) is about aligning the representation format of data so that garbled text is avoided when exchanging data with other systems. What normalization deals with is the logical design of how tables and items are divided; which code is used to represent a value is not the subject of normalization.
Incorrectエ
Encryption is a security measure that converts data into a form third parties cannot read, in order to protect confidentiality. Normalization does not conceal the content of the data; it is a design technique that organizes the structure so that the data is easier to handle, so its purpose is different.
ここがポイント
- The purpose of normalization is to eliminate duplicated data (redundancy) so as to prevent contradictions such as update anomalies, and to keep the data in a state that is easy to change, that is, to improve maintainability. The basic idea is to split tables up by relationship and have the other tables refer to them by primary key.
- Normalization is, after all, only a matter of the logical design of table structure; do not confuse it with other technologies that serve different purposes, such as checksums (error detection), unified character encoding (uniform representation format), or encryption (ensuring confidentiality).
用語