数据库范式5nf-第五范式（5NF）数据库管理系统.pdf

数据库范式5nf_第五范式（5NF）数据库管理系统 数据库范式5nf Fifth normal form (5NF) Fifth normal form (5NF) is also known as project-join normal form (PJ/NF) project-join normal form (PJ/NF). It is designed to minimize redundancy in relational databases by separating semantically connected relationships in multiple formats to store multi-valued facts. 第五范式(5NF) 第五范式(5NF)也称为投影联合范式(PJ / NF) 投影联合范式(PJ / NF) 。 它旨在通过以多种格式分隔语义连接的关系来存储多值事实，以最⼤程度地减少关系 数据库中的冗余。 A relation R R is in 5NF 5NF if and only if every non-trivial join dependency in R R is implied by the candidate keys of R R. A relation break up into two relations must contain lossless join Property, which makes certain that no invalid or extra tuples of attributes are created when relations are again joined together through a natural join. 关系R R是5NF 5NF当且仅当每⼀个不平凡的连接依赖于R R由R R的候选键暗⽰。 分解为两个关系的关系必须包含⽆损连接属性，这可以确保在通过 ⾃然连接将关系再次连接在⼀起时，不会创建任何⽆效或多余的元组。 Properties: Properties: 特性： 特性： A relation R R with attributes, its values and tuples is in 5NF 5NF if and only if the following conditions are satisfied, 当且仅当满⾜以下条件时，带有属性，其值和元组的关系R R的值为5NF 5NF ： 1. The relation R R should be already in . 关系R R应该已经在 。 2. The relation R R cannot be additionally non loss decomposed (join dependency). 关系R R不能另外进⾏⾮损耗分解(联接依赖)。 If the relation or table can further decompose to remove redundancy and anomaly, and when the process of rejoining followed the decomposed tables through the means of candidate keys, we should not be losing the original data or any new record set should not arise. Understandably, joining two or more decomposed table should not lose records or create new records. 如果关系或表可以进⼀步分解以消除冗余和异常，并且当重新连接的过程通过候选键的⽅式遵循分解后的表时，我们不应丢失原始数据，也 不应出现任何新的记录集。 可以理解，联接两个或多个分解表不应丢失记录或创建新记录。 Join dependency Join dependency 连接依赖 连接依赖 A table or relation can be recreated or re-designed by joining multiple tables and each table of this contain a subset of the attributes and values of the table, then the table is in Join Dependency. It is a generalization of Multivalued Dependency