Database Reference

In-Depth Information

5.2.1 Transitive dependence

Z is transitively dependent on X when X determines Y and Y determines Z.

Transitive dependence thus describes that Z is indirectly dependent on X through its

relationship with Y.

Here is the transitivity rule restated:

Given X Y

Given Y Z

Then X Z

5.2.2 The Reflexive Rule

If X is a composite, composed of A and B, then X A and X B.

Example:

X = Name, City. Then we are saying that X Name and X City.

The rule, which seems quite obvious, says if I give you the combination <Sachin, Amrit-

sar>, what is this person's Name? What is this person's City?

5.2.3 The Augmentation Rule

If X Y, then XZ Y. You might call this rule, “more information is not really needed,

but it doesn't hurt.”

5.2.4 The Decomposition Rule

The decomposition rule says that if it is given that X YZ (that is, X defines both

Y and Z), then X Y and X Z.