Everyone,

Here's an example of denormalization as a valid design technique.

In a Custoemr table you have moved the City and State fields to a related ZipCode table with the join based on the ZipCode in teh customer table. You did this to achieve 3rd Normal Form (All fields are dependent on ONLY the PK) when you realized that City and State were codependent on ZipCode and the PK.

Your system is used to print 10,000,000 mailing labels once a week. Your tesint finds that a lable printed from a two table join as comapred to a single table operation takes an exteremly longer time to process. You determine that teh label printing is more of an isue than the update anomaly possibilities so you decide to denormalize and put the city and state fields in the customer table directly. You have denormalized the structure of the Customer table because it is not in 3rd normal form any longer. However you ahve done it for a valid reason.

The fact that you went all the way to fully normalized before backed off for a specific reason has given you the ZipCode table for data entry validation and for correcting any update anomalies that may occur.