"Database Normalization"
Database Normalization is the process of efficiently organizing data in a database.
There are two goals of the normalization process — eliminate redundant data and ensure logical data dependencies.
The database community has developed a series of guidelines for ensuring that databases are normalized. These are referred to as normal forms and are numbered from one (1NF) through five (5NF). In practical applications, 1NF through 4NF are typically used. Fifth normal form (5NF) is very rarely seen.
First normal form (1NF) sets the very basic rules for an organized database:
- Eliminate duplicative columns from the same table
- Create separate tables for each group of related data and identify each row with a unique column or set of columns
Second normal form (2NF) further addresses the concept of removing duplicative data:
- Meet all the requirements of the first normal form
- Remove subsets of data that apply to multiple rows of a table and place them in separate tables
- Create relationships between these new tables and their predecessors through the use of foreign keys
Third normal form (3NF) goes one step further:
- Meet all the requirements of the second normal form
- Remove columns that are not dependent upon the primary key
Fourth normal form (4NF) has one additional requirement:
- Meet all the requirements of the third normal form
- A relation is in 4NF if it has no multi-valued dependencies
Normalization guidelines are cumulative. For a database to be in 2NF, it must first fulfill all the criteria of a 1NF database.