Release 10.1A: OpenEdge Getting Started:
Database Essentials

Denormalization

Denormalizing a database means that you reintroduce redundancy into your database in order to meet processing requirements.

To reduce Table 2–8 to the third normal form, you eliminated the Total After Tax column because it contains data that can be derived. However, when you consider data access requirements, you discover that this data is constantly used. Although you can construct the Total After Tax value, your customer service representatives need this information immediately, and you do not want to have to calculate it every time you need it. If you keep it in the database, it is always available on request. In this instance, the performance outweighs other considerations, so you denormalize the data by including the derived field in the table.