what is normalization ? what is need of normalization and what are the types of normalization?

 What is normalization in DBMS?

Normalization is a property of database to reduce or minimize  the redundancy and anomalies by decomposing the database table . Normalization is the step by step decomposition of one relation into sub-relation to achieve highest normal form.

Importance of Normalization:

• Used to reduce redundancy or repeating value.
• Used to reduce anomalies.
• Used to de-centralization of data.
• Used to minimize the null value.

Types of Normalization:

1. First normal form (1NF)
2. Second normal form (2NF)
3. Third normal form (3NF)
4. Boyce Codd normal form (BCNF) 
5.  Fourth normal form (4NF)
6. Fifth normal form (5NF)

First normal form (1NF) :  A relation is said to be in first normal form if it not contain any repeating groups. each value  should be single .  There are two methods to solve 1NF

1. Flattering of table : In this method we remove the repeating groups filling in the missing entry of each incomplete row of the tables with the copy of their corresponding null  repeating attributes.
2. Decomposition of table : In this approach we decompose the table into new table   by certain rules.

• rule -1 : One of the table contains primary key of original table + all the non-repeating attributes. non repeating attribute for example :course code , course name .
• rule-2 : The other table contains the copy of primary key + all the repeating attributes. example of repeating attributes : student name , teacher name .

Second normal form (2NF) : A relation is said to be in 2NF if it is in 1NF and should not contain any partial dependency .

Third normal form (3NF) : A relation is said to be in 3NF if it is in 2NF and should not contain any transitive dependency.

Boyce Codd normal form (BCNF) : A relation is said to be in BCNF if it is in 3NF  and L.H.S of functional dependency must contain candidate key or Super key. 

Fourth normal form (4NF) : A relation is said to be in 4NF if it is in 3NF or BCNF form . and it should not contain multivalued dependency.  Multivalued dependency is the dependency where one attribute derives more attribute.

example :      Customer name (X)        City (Y)

                          RAM                            NEW DELHI

                          RAM                             MUMBAI

                          SITA                             MUMBAI

Here X multi determines Y. 

Fifth normal form (5NF) : A relation is said to in 5NF if it is in 4NF. it should not have join dependency and also the joining must be lossless. a join dependency is a constraint on the set of legal relations over a database scheme.