Chapter 6 Normalization

Third normal form
A relation schema S = (R, F) is in the third
normal form if it is in 2NF and, for every FD
X → Y ∈ F, either of the following is true
1) Y ⊆ X; or X is a superkey of R; 2)each attribute
in A ∈ Y −X belongs to some candidate
key K of R.
It is clear that BCNF is a special case of 3NF.
Thus, every schema in BCNF is automatically
in 3NF, while the other direction does not need
to be true.
The schema HasAccount(AccountNumber, ClientID,
OfficeID), with its primary key being {ClientID,
OfficeID}, and the FD AccountNumber → OfficeID
is not in BCNF, since AccountNumber is not a
superkey.
However, since OfficeID is part of the key, this
schema is in 3NF.
Homework: 6.2
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