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Normalization and Denormalization
Posted Date: 30 May 2008 Resource Type: Definitions Category: General
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Posted By: rudra Member Level: Silver
Rating:  Points: 5
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Normalization
Normalization theory is built the concept of normal forms. Normalizations reduces redundancy. Redundancy is unnecessary repetition of data. It can cause problems with storage and retrieval of data. During the process of normalization, dependencies can be identified, which can cause problems during deletion and updation. Normalization theory is based on the fundamental notation of functional dependency. Normalization helps in simplifying the structure of tables.
Suppose for an entity customer if attributes like cunno, name, address are required, then it can be perceived that for a particular cusno, only one name and address is possible. Hence the attribute name, address are said to be functionally dependent on the attribute cusno. There are four levels of normalization.
Denormalization
Normalization helps in reducing redundancy. But at times when information is required from more than one table, at a faster rate, it is wiser to introduce some amount of redundancy in the table. This intentional introduction of redundancy in to the table is called Denormalization.
For example, if the query were used to display the names of students and their marks obtained in each subject, then it would be advisable to maintain information about the students. Otherwise, every time such a query is made, a join will have to be carried out on the two tables. For the sake of better performance some amount of redundancy has to be introduced.
The language widely used in relational database is Structured Query Language, more popularly known as SQL. It is the standard relational database access language. They can be roughly divided in to three categories based on their functions namely Data Definition Language, Data Manipulation Language and Data Control Language.
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