第二归一化阶段和第三归一化阶段之间的差异 [英] Difference between 2nd normalization phase and 3rd normalization phase

问题描述

我已经将一些表正规化为第二个正常形式。

以下是规范化的表格。

我真的困惑于3正规化阶段，因为它是一些类似于第二正规化阶段。我的问题是，护士表已经在第三个正常化阶段了吗？

也可以有人解释我，第二个正规化形式和3归一化形式。
我知道第二个归一化形式具有部分依赖性，第三个归一化形式具有传递依赖性，但仍然有点混乱。

谢谢您的时间。 p>

解决方案

2NF和3NF之间的区别是这个。假设一些关系满足形式A-> B的非平凡函数依赖性，其中B是非初级属性。如果A不是超级键，则违反

2NF但是是候选键的正确子集

$ b p>超级键只是指包括您的表的候选键的任何属性集。

因此，如果关系满足3NF，那么它已经满足2NF。在这个意义上，2NF本身并不是特别重要。实际上3NF也不是特别重要。 Boyce-Codd Normal Form更重要，但我猜这是家庭作业，你应该先学习2NF和3NF。

没有人能确定你的设计是否满足3NF或者不是因为你没有说过它应该满足的依赖关系。根据你的属性的名称，你的设计似乎不太可能是正确的。看来，护士一次只能分配一个病人，我想这不是正确的。

I have normalized some tables up to 2nd normal form.

Below are the normalized tables.

I am really confused with the 3 normalization phase as it is some what similar to 2nd normalization phase. My question is, is the nurse table already in the 3rd normalization phase or not ?

Also can some one explain me , what is the difference between the 2nd normalization form and 3 normalization form. I know that 2nd normalization form has partial dependencies and 3rd normalization form has transitive dependencies but still am a bit confused.

Thank you for your time.

解决方案

The difference between 2NF and 3NF is this. Suppose that some relation satisfies a non-trivial functional dependency of the form A->B, where B is a nonprime attribute.

2NF is violated if A is not a superkey but is a proper subset of a candidate key

3NF is violated if A is not a superkey

"Superkey" just means any set of attributes that includes a candidate key of your table.

Therefore if a relation satisfies 3NF then it already satisfies 2NF. In that sense, 2NF itself is not especially important. Actually 3NF is not especially important either. Boyce-Codd Normal Form is more important but I guess this is homework and you are expected to study 2NF and 3NF first.

No one can say for sure whether your design satisfies 3NF or not because you haven't said what dependencies it is supposed to satisfy. Judging by the names of your attributes it seems unlikely that your design is correct. It appears that a nurse can only be assigned one patient at a time, which I guess would not be right.

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