Describe the purpose of using inference rules to identify functional dependencies for a given relation.

Question

What will be an ideal response?

Answer 1

Even if we restrict our attention to nontrivial functional dependencies with one-to-one (1:1)
relationships that hold for all time, the complete set of functional dependencies for a given
relation can still be very large. It is important to find an approach that can reduce that set to a
manageable size. Ideally, we want to identify a set of functional dependencies (represented as
X) for a relation that is smaller than the complete set of functional dependencies (represented
as Y) for that relation and has the property that every functional dependency in Y is implied by
the functional dependencies in X. Hence, if we enforce the integrity constraints defined by the
functional dependencies in X, we automatically enforce the integrity constraints defined in the
larger set of functional dependencies in Y. This requirement suggests that there must be
functional dependencies that can be inferred from other functional dependencies. For example,
functional dependencies A ? B and B ? C in a relation implies that the functional dependency
A ? C also holds in that relation. A ? C is an example of a transitive functional dependency.
How do we begin to identify useful functional dependencies on a relation? Normally, the
database designer starts by specifying functional dependencies that are semantically obvious;
however, there are usually numerous other functional dependencies. In fact, the task of
specifying all possible functional dependencies for ‘real’ database projects is more often than
not, impractical. However, in this section we do consider an approach that helps identify the
complete set of functional dependencies for a relation and then discuss how to achieve a
minimal set of functional dependencies that can represent the complete set.