是候选关键决定因素对于BCNF是否足够好？ [英] Is a candidate key determinant good enough for BCNF?

问题描述

我的家庭作业中出现的问题如下：

A question that came up in my homework is as follows:

• 如果行列式是候选键的一部分，足够用于BCNF？

我不这么认为，因为如果所有非关键属性都取决于整个关系，主键，没有别的。这说明行列式是候选键的部分，所以这意味着部分功能依赖吗？

I don't think so, because a relation is in BCNF if all non-key attributes depend on the whole primary key, and nothing else. This says the determinant is part of a candidate key, so does this imply a partial functional dependency?

但是，我开始第二次猜到自己因为候选键可能是超级键，但似乎不是这样。

However, I began to second guess myself because there's a possibility that the candidate key is a super key, but it doesn't seem like that is the case.

你觉得怎么样？

推荐答案

part的意思是什么？一些但不是全部？部分或全部？

What does the question mean by "part"? Some but not all of? Some or all of? What do you mean by it?

部分函数依赖关系的定义使用partial来表示一些而不是全部。

The definition of partial functional dependency uses "partial" to mean some but not all of.

检查BCNF的定义。要求没有非主要属性部分功能上依赖于任何键的那个也需要除了你写的其他事情。所以你的如果是不正确的。但是如果分配问题的部分是指部分但不是全部，如在部分依赖，则通过BCNF的相关定义，该关系不在BCNF中。

Check definitions of BCNF. The one that requires that no non-prime attribute be partially functionally dependent on any key also requires other things than you wrote. So your "if" is not correct. But if the assignment question's "part" means "part of but not all of" as in "partially dependent" then by the relevant definition of BCNF the relation is not in BCNF.

所有候选键都是超级键。但候选键是不包含任何较小超级键的超级键。超级键涉及BCNF的定义的不同形式。但如果BCNF根据一个定义和你知道的违反，它不可能被另一个定义。

All candidate keys are superkeys. But the candidate keys are the superkeys that do not contain any smaller superkeys. Superkeys are involved in a different form of the definition of BCNF. But if BCNF is violated according to one definition and what you know, it can't possibly be allowed by another one.

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