Chapter 6 Normalization

3. Duplicated data does not always mean redundancy.
Given the following value of the
aforementioned table R and
A B C D
1 1 3 4
2 1 3 4
It seems that it contains redundancy since the
two tuples only differs on A.
But, since there is no FD over the attribute set
of B, C and D, there can’t be any redundancy
from a technical perspective. It would contain
redundancy if {A, B} is a key, and B → C,D is
a FD.
Thus, redundancy depends on both factors of
a schema: data and the associated FD set.
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