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第一范式(1NF) 标准的表
第二范式(2NF) 部分函数依赖
第三范式(3NF) 传递函数
BC范式(BCNF) 候选键相关
第四范式(4NF) 消除多值依赖
第五范式(5NF)
1NF的定义
如果关系模式R的每一个属性都是不可再分的数据项，则称关系模式R满足第一范式。
A relation in which that intersection of each row and column contains one and
only one value.
2NF的定义
若R满足第一范式，且每一个非主属性完全函数依赖于主码，则R满足第二范式。
A relation that is in first normal form and every non-primary-key attribute
is fullyfunctionally dependent on the primary key.
3NF的定义
若R满足第二范式，且每一个非主属性都不传递函数依赖于主码，则R满足第三范式。
A relation that is in first and second normal form , and in which no
non-primary-keyattribute is transitively dependent on the primary key
4 BC范式（BCNF）
若R满足第三范式，且每一个主属性都不部分函数依赖或传递函数依赖于主码，则R满足第三范式。
每一个决定属性集（因素）都包含（候选）码
R中的所有属性（主，非主属性）都完全函数依赖于码
由BCNF的定义可以得到结论，一个满足BCNF的关系模式有：
（1）所有非主属性对每一个码都是完全函数依赖；
（2）所有的主属性对每一个不包含它的码，也是完全函数依赖；
（3）没有任何属性完全函数依赖于非码的任何一组属性。
A relation is in BCNF if and only if every determinant is a candidate key (we
identify all the determinants and make sure that they are candidate keys, )
