寻找R的钥匙
R = {A, B, C, D, E, F, G, H, I, J}
F =
{{A,B} -> {C},
{A}-> {D,E},
{B} -> {F},
{C}-> {B},
{F}->{G,H},
{D}->{I,J}
问题是：R 的关键是什么？
我认为根据问题的表述方式，他们希望我找到一个候选键。
如果我有 AB+，我可以确定关系中的所有属性，这意味着 AB 是一个超级密钥。超级密钥 AB 的真子集 {A} 和 {B} 不是超级密钥，因此为什么 AB 是候选密钥。但据我所知，如果我们有 AC+，我们还可以找到另一个候选键。这是正确的还是我在某个地方犯了错误？
R = {A, B, C, D, E, F, G, H, I, J}
F =
{{A,B} -> {C},
{A}-> {D,E},
{B} -> {F},
{C}-> {B},
{F}->{G,H},
{D}->{I,J}
The question is: What is the key for R?
I assume based on how the question has been formulated that there is one single candidate key which they want me to find.
If i have AB+ i can determine all the attributes in the relation meaning AB is a superkey. The proper subsets of the superkey AB which are {A} and {B} are not superkeys, hence why AB then is a candidate key. But from what i can tell there is another candidate key aswell which we can find if we have AC+. Is this correct or am i making a mistake somewhere?
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是的，你是对的：假设
F是R依赖关系的覆盖，该关系有两个候选键：{A, B}和{A, C}。通过计算
{A,B}+和{A,C}+可以轻松显示这一点。Yes, you are correct: assuming that
Fis a cover of the dependencies ofR, the relation has two candidate keys:{A, B}and{A, C}.This can be easily shown by computing both
{A,B}+and{A,C}+.