Describe the concept of multi-valued dependency and describe how this concept relates to 4NF. Provide an example to illustrate your answer.
What will be an ideal response?
Multi-valued Dependency (MVD) Represents a dependency between attributes (for
example, A, B, and C) in a relation, such that for each value of A there is a set of values for B
and a set of values for C. However, the set of values for B and C are independent of each
other.
A multi-valued dependency can be defined as being trivial or nontrivial. A MVD A
???? B in relation R is defined as being trivial if (a) B is a subset of A or (b) A ? B = R.
A MVD is defined as being nontrivial if neither (a) nor (b) are satisfied. A trivial MVD does
not specify a constraint on a relation, while a nontrivial MVD does specify a constraint.
Fourth Normal Form (4NF) A relation that is in Boyce-Codd Normal Form and
contains no nontrivial multi-valued dependencies.
Fourth normal form (4NF) is a stronger normal form than BCNF as it prevents relations from
containing nontrivial MVDs, and hence data redundancy. The normalization of BCNF
relations to 4NF involves the removal of the MVD from the relation by placing the
attribute(s) in a new relation along with a copy of the determinant(s).
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