Problems Discussed in this chapter

 Question 4: Describe the concept of functional dependency. How is this associated with the process of normalization?

 Answer 4:    The term functional dependency and functional dependency are used  interchangeably in the literature. We may use example the shipment, one  that includes the usual attributes S#, P#, QTY and CITY.

Let r be  a relation, and let X and Y be arbitrary subsets of the set of attributes of r. Then we say that Y is a Functional dependent of X in symbols. 

 X->Y

 If and only if each X value in r has associated with it precisely one y value  in r.

In other words, whenever two tuples or r agree on their X value, they  also agree on their Y values.

For example the relation shown in figure satisfied the functional dependency

                     {S#}->{CITY}

because every tuple of the relation with a given S# value also has the same  CITY value.

A functional dependency is a many-to-one relationship between two sets of attributes of a given relvar. Given a relvar R, the functional dependency

A->B is said to hold for R if and only if, whenever two tuples of R have the same value for A, they also have the same value for B. every relvar necessarily satisfies certain trivial functional dependencies.

Functional dependency is trivial if and right-hand side that is dependent is a subset of the left hand side that is the determinant.