Chapter 6 Normalization

A couple of points
1. A BCNF can have more than one candidate
keys. For example, R = (ABCD, F), where
F = {AB → CD, AC → BD}, has two keys, AB
and AC. R is still in BCNF, since the determinant
of both FDs are superkeys, although they
are different.
2. Redundancy arises when the values of some
attribute(s) X necessarily implies the values of
other attribute(s) A, because of a FD X → A.
For example, since SSN → Name, the information
on Name is redundant in the following
structure.
SSN Name Address Hobby
1111 John Doe 123 Main St. Stamps
1111 John Doe 123 Main St. Coins
2222 Mary Doe 7 Lake Dr. Acting
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