10.2: Normal Forms

The normal forms usually of interest to the database designer are 1NF, 2NF, 3NF and BCNF. There are more (higher) normal forms that we leave to follow-up courses. We discuss 1NF and BCNF; 2NF and 3NF are mentioned in our summary. 1NF is so important, it is actually a property of a relation; that is, to say something is a relation means that it is at least in 1NF. BCNF has a simple definition (compared to 2NF and 3NF) and is the usual objective of the designer.

If you understand 1NF and BCNF then you have good insight into the nature of relations that are easy to understand and maintain. If you understand why a relation is not BCNF then you will know the source of its redundant data, which is necessary to know how to properly maintain the data contained in the relation. In most practical cases when a relation is not BCNF the reason will be related to partial or transitive dependencies. 2NF relations do not have partial dependencies, and 3NF relations do not have partial nor transitive dependencies.