Database normalization

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In relational database design, the process of organizing data to minimize redundancy is called normalization or the process of decomposing relation with anomalies to produce smaller,well-structured relation. Normalization usually involves dividing a database into two or more tables and defining relationships between the tables. The objective is to isolate data so that additions, deletions, and modifications of a field can be made in just one table and then propagated through the rest of the database via the defined relationships.

Edgar F. Codd, the inventor of the relational model, introduced the concept of normalization and what we now know as the First Normal Form (1NF) in 1970.[1] Codd went on to define the Second Normal Form (2NF) and Third Normal Form (3NF) in 1971,[2] and Codd and Raymond F. Boyce defined the Boyce-Codd Normal Form (BCNF) in 1974.[3] Higher normal forms were defined by other theorists in subsequent years, the most recent being the Sixth normal form (6NF) introduced by Chris Date, Hugh Darwen, and Nikos Lorentzos in 2002.[4]

Informally, a relational database table (the computerized representation of a relation) is often described as "normalized" if it is in the Third Normal Form.[5] Most 3NF tables are free of insertion, update, and deletion anomalies, i.e. in most cases 3NF tables adhere to BCNF, 4NF, and 5NF (but typically not 6NF).

A standard piece of database design guidance is that the designer should create a fully normalized design; selective denormalization can subsequently be performed for performance reasons.[6] However, some modeling disciplines, such as the dimensional modeling approach to data warehouse design, explicitly recommend non-normalized designs, i.e. designs that in large part do not adhere to 3NF.[7]


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