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## What is the need for normalization?.Database Management Systems - 10CS54 VTU notes (JUN/JULY 2013/Jan 2016)

Explain the first,second and third normal forms with examples?

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The purpose of normalization.
• The problems associated with redundant data.
• The identification of various types of update anomalies such as insertion, deletion, and modification anomalies.
• How to recognize the appropriateness or quality of the design of relations.
• The concept of functional dependency, the main tool for measuring the appropriateness of attribute groupings in relations.
• How functional dependencies can be used to group attributes into relations that are in a known normal form.
• How to define normal forms for relations.  • How to undertake the process of normalization. • How to identify the most commonly used normal forms, namely first (1NF), second (2NF), and third (3NF) normal forms, and Boyce-Codd normal form (BCNF). • How to identify fourth (4NF), and fifth (5NF) normal forms.
First Normal Form (1NF)
First normal form is now considered to be part of the formal definition of a relation; historically, it was defined to disallow multivalued attributes, composite attributes, and their combinations. It states that the domains of attributes must include only atomic (simple, indivisible) values and that the value of any attribute in a tuple must be a single value from the domain of that attribute. Practical Rule: "Eliminate Repeating Groups," i.e., make a separate table for each set of related attributes, and give each table a primary key. Formal Definition: A relation is in first normal form (1NF) if and only if all underlying simple domains contain atomic values only.
Second Normal Form (2NF) Second normal form is based on the concept of fully functional dependency. A functional X Y is a fully functional dependency is removal of any attribute A from X means that the dependency does not hold any more. A relation schema is in 2NF if every nonprime attribute in relation is fully functionally dependent on the primary key of the relation. It also can be restated as: a relation schema is in 2NF if every nonprime attribute in relation is not partially dependent on any key of the relation.
Third Normal Form (3NF) Third normal form is based on the concept of transitive dependency. A functional dependency X Y in a relation is a transitive dependency if there is a set of attributes Z that is not a subset of any key of the relation, and both X Z and Z Y hold. In other words, a relation is in 3NF if, whenever a functional dependency

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