normalization have a se veral forms that a database structure can be subject to, each with rules that constrain the database further and each creating what is called a Normal Form. These are, in order:
> First Normal Form (1NF)
> Second Normal Form (2NF)
> Third Normal Form (3NF)
> Boyce Codd Normal Form (BCNF)
> Fourth Normal Form (4NF)
> Fifth Normal Form (5NF)
> Optimal Normal Form (ONF)
> Domain-Key Normal Form (DKNF)
Theses are defined as :
> 1NF: Eliminate Repeating Groups : Make a separate table for each set of related attributes, and give each table a primary key. Each field contains at most one value from its attribute domain.
> 2NF: Eliminate Redundant Data : If an attribute depends on only part of a multi-valued key, remove it to a separate table.
> 3NF: Eliminate Columns Not Dependent On Key : If attributes do not contribute to a description of the key, remove them to a separate table. All attributes must be directly dependent on the primary key.
> BCNF: Boyce-Codd Normal Form : If there are non-trivial dependencies between candidate key attributes, separate them out into distinct tables.
> 4NF: Isolate Independent Multiple Relationships : No table may contain two or more 1:n or n:m relationships that are not directly related.
> 5NF: Isolate Semantically Related Multiple : Relationships There may be practical constrains on information that justify separating logically related many-to-many relationships.
> ONF: Optimal Normal Form : A model limited to only simple (elemental) facts, as expressed in Object Role Model notation.
> DKNF: Domain-Key Normal Form : A model free from all modification anomalies.