Normalization or data normalization is a process to organize the data into tabular format (database tables). A good database design includes the normalization, without normalization a database system may slow, inefficient and might not produce the expected result. Normalization reduces the data redundancy and inconsistent data dependency.
Normal FormsWe organize the data into database tables by using normal forms rules or conditions. Normal forms help us to make a good database design. Generally we organize the data up to third normal form. We rarely use the fourth and fifth normal form.
To understand normal forms consider the folowing unnormalized database table. Now we will normalize the data of below table using normal forms.
First Normal Form (1NF)A database table is said to be in 1NF if it contains no repeating fields/columns. The process of converting the UNF table into 1NF is as follows:
- Separate the repeating fields into new database tables along with the key from unnormalized database table.
- The primary key of new database tables may be a composite key
Second Normal Form (2NF)A database table is said to be in 2NF if it is in 1NF and contains only those fields/columns that are functionally dependent(means the value of field is determined by the value of another field(s)) on the primary key. In 2NF we remove the partial dependencies of any non-key field.
The process of converting the database table into 2NF is as follows:
- Remove the partial dependencies(A type of functional dependency where a field is only functionally dependent on the part of primary key) of any non-key field.
- If field B depends on field A and vice versa. Also for a given value of B, we have only one possible value of A and vice versa, Then we put the field B in to new database table where B will be primary key and also marked as foreign key in parent table.
Third Normal Form (3NF)A database table is said to be in 3NF if it is in 2NF and all non keys fields should be dependent on primary key or We can also said a table to be in 3NF if it is in 2NF and no fields of the table is transitively functionally dependent on the primary key.The process of converting the table into 3NF is as follows:
- Remove the transitive dependecies(A type of functional dependency where a field is functionally dependent on the Field that is not the primary key.Hence its value is determined, indirectly by the primary key )
- Make separate table for transitive dependent Field.
Boyce Code Normal Form (BCNF)A database table is said to be in BCNF if it is in 3NF and contains each and every determinant as a candidate key.The process of converting the table into BCNF is as follows:
- Remove the non trival functional dependency.
- Make separate table for the determinants.
Fourth Normal Form (4NF)A database table is said to be in 4NF if it is in BCNF and primary key has one-to-one relationship to all non keys fields or We can also said a table to be in 4NF if it is in BCNF and contains no multi-valued dependencies.The process of converting the table into 4NF is as follows:
- Remove the multivalued dependency.
- Make separate table for multivalued Fields.
Fifth Normal Form (5NF)A database table is said to be in 5NF if it is in 4NF and contains no redundant values or We can also said a table to be in 5NF if it is in 4NF and contains no join dependencies.The process of converting the table into 5NF is as follows:
- Remove the join dependency.
- Break the database table into smaller and smaller tables to remove all data redundancy.