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Database_normalization - Database normalization From...

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Database normalization From Wikipedia, the free encyclopedia Jump to: navigation , search In the design of a relational database management system ( RDBMS ), the process of organizing data to minimize redundancy is called normalization . The goal of database normalization is to decompose relations with anomalies in order to produce smaller, well-structured relations. Normalization usually involves dividing large tables into smaller (and less redundant) tables and defining relationships between them. 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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Contents 1 Objecti ves of normali zation 1 . 1 F r e e t h e d a t a b a s e o f m o d i f i c a t i o n a n o m a l i
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[ edit ] Objectives of normalization A basic objective of the first normal form defined by Codd in 1970 was to permit data to be queried and manipulated using a "universal data sub-language" grounded in first-order logic . [8] ( SQL is an example of such a data sub-language, albeit one that Codd regarded as seriously flawed.) [9] The objectives of normalization beyond 1NF (First Normal Form) were stated as follows by Codd: 1. To free the collection of relations from undesirable insertion, update and deletion dependencies;
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2. To reduce the need for restructuring the collection of relations as new types of data are introduced, and thus increase the life span of application programs; 3. To make the relational model more informative to users;
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4. To make the collection of relations neutral to the query statistics, where these statistics are liable to change as time goes by.
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