Database Normalization

Database normalization is a technique used in designing relational database tables to minimize duplication of information thereby protecting the database against certain types of logical or structural problems.

For example, when multiple instances of a data item occur in a table, it is possible for these instances to not remain consistent when the data within the table is updated. This results in a loss of data integrity.

A table that is sufficiently normalized is less vulnerable to such data anomolies because its structure follows basic assumptions where multiple occurences of the same information should be represented as a single instance only.

The payment for this is that more tables are required and more joins, reducing performance. For this reason, highly normalized tables are typically used in database applications involving many isolated transactions; less normalized tables tend are used when complex relationships between data entities and data attributes must be mapped.

Normalization is described in degrees of strictness. Each table has a "highest normal form" [HNF]. A 3NF inherits higher norms [2NF]. but the reverse does not apply.

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