March 2022
Intermediate to advanced
682 pages
22h 58m
English
A functional dependency (FD) is a type of relationship between attributes, as described in the following definition:
Definition: If R is a relation schema and A and B are non-empty sets of attributes in R, we say that B is functionally dependent on A if, and only if, each value of A in R has associated with it exactly one value of B in R.
We write this as
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which we read as “A functionally determines B.” The definition says that if two tuples in an extension of R have the same value for A, they must also have the same values for B. More formally, for every pair of tuples, t1 and t2, in every instance of R, we have ...