Problem solve Get help with specific problems with your technologies, process and projects.

Functional dependencies

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 --> 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 editor@searchDatabase.com 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.

Dig Deeper on Oracle database design and architecture

Start the conversation

Send me notifications when other members comment.

Please create a username to comment.