Introduction to database management systems

Database Normalization is a technique of organizing data in databases. Normalization is a systematic approach of decomposing tables to eliminate data redundancy and undesirable characteristics like Insert, Update and Delete. Normalization is used for mainly two purpose, 

• Eliminating redundant (useless) data.
• Ensuring data dependencies.

Normalization rule are divided into following normal form.

• First Normal Form
• Second Normal Form
• Third Normal Form
• BCNF

First Normal Form (1NF)

A relation is first normal form if it meets below criteria:

• Each attribute (column) value must be a single value only.
• All values for a given attribute (column) must be of the same type.
• Each attribute (column) name must be unique.
• No two tuples (rows) in a relation can be identical.
• The order of tuples (rows) is insignificant.

Second Normal Form (2NF)

A relation is second normal form if it meets below criteria:

• A relation is in second normal form (2NF) if all of its non-key attributes are dependent on all of key.
• Relations that have a single attribute for a key are automatically in 2NF.

Third Normal Form (3NF)

• A relation is in third normal form (3NF) if it is in second normal form and it contains no transitive dependencies.
• Consider relation R containing attributes A, B and C. R (A, B, C)
• If A → B and B → C then A → C
• Transitive Dependency: Three attributes with above dependencies.

Boyce-Codd Normal Form (BCNF)

A 3NF table which does not have multiple overlapping candidate keys is said to be in BCNF.For a table to be in BCNF, following conditions must be satisfied:

• R must be in 3rd Normal Form
• and, for each functional dependency ( X -> Y ), X should be a super Key.