问题
I've gone through internet and books and still have some difficulties on how to determine the normal form of this relation
R(a, b, c, d, e, f, g, h, i)
FDs =
B→G
BI→CD
EH→AG
G→DE
So far I've got that the only candidate key is BHI (If I should count with F, then BFHI). Since the attribute F is not in use at all. Totally independent from the given FDs.
- What am I supposed to do with the attribute F then?
- How to determine the highest normal form for the realation R?
回答1:
What am I supposed to do with the attribute F then?
You could observe the fact that the only FD in which F gets mentioned, is the trivial one F->F. It's not explicitly mentioned precisely because it is trivial. Nonetheless, all of Armstrong's axioms apply to trivial ones equally well. So, you can use this trivial one, e.g. applying augmentation, to go from B->G to BF->GF;
How to determine the highest normal form for the relation R?
first, test the condition of first normal form. If satisfied, NF is at least 1. Check the condition of second normal form. If satisfied, NF is at least 2. Check the condition of third normal form. If satisfied, NF is at least three.
Note :
"checking the condition of first normal form", is a bit of a weird thing to do in a formal process, because there exists no such thing as a formal definition of that condition, unless you go by Date's, but I have little doubt that your course does not follow that definition.
Hint :
Given that the sole key is BFHI, which is the first clause of "the key, the whole key, and nothing but the key" that gets violated by, say, B->G ?
来源：https://stackoverflow.com/questions/9402650/how-to-find-the-highest-normal-form-for-a-given-relation