My question is related to functional dependencies. I would like to know an example of a relation for which the following result is not true:
a -->

    Requires Free Membership to View

b and c --> b implies a --> c.

This is one of the more interesting pieces of functional decomposition to learn to understand. I'll use simple mathematics for an example.

If we start with the following assertions (functions):

A: 1 = n modulo 2
B: n is an integer
C: 0 = n modulo 2

The only class of numbers that satisfy A is odd integers. The only class of numbers that satisfies C is even integers. Any n that satisfies A implicitly satisfies B. Any n that satisfies C implicitly satisfies B. No n that satisfies A will ever satisfy C.

For More Information

  • What do you think about this answer? E-mail the editors at with your feedback.
  • The Best Database Design Web Links: tips, tutorials, scripts, and more.
  • Have an Oracle or SQL tip to offer your fellow DBAs and developers? The best tips submitted will receive a cool prize. Submit your tip today!
  • Ask your database design -- or help out your peers by answering them -- in our live discussion forums.
  • Ask the Experts yourself: Our SQL, database design, Oracle, SQL Server, DB2, metadata, object-oriented and data warehousing gurus are waiting to answer your toughest questions.

This was first published in May 2002

There are Comments. Add yours.

TIP: Want to include a code block in your comment? Use <pre> or <code> tags around the desired text. Ex: <code>insert code</code>

REGISTER or login:

Forgot Password?
By submitting you agree to receive email from TechTarget and its partners. If you reside outside of the United States, you consent to having your personal data transferred to and processed in the United States. Privacy
Sort by: OldestNewest

Forgot Password?

No problem! Submit your e-mail address below. We'll send you an email containing your password.

Your password has been sent to: