Normalization is a method of break down complex table’s structure into simple table structure by using certain rules. Normalization usually involves dividing a database into two or more tables and defining relationships between the tables. Normalization is the process of efficiently organizing data in a database. There are two goals of the normalization process: eliminating redundant data and ensuring data dependencies make sense. Both of these are worthy goals as they reduce the amount of space a database consumes and ensure that data is logically stored.
The Normal Forms
Normalization results in the formation of tables that fulfill certain specified rules and represents certain normal forms. The database community has developed a series of guidelines for ensuring that databases are normalized. The normal forms are used to ensure inconsistencies are not introduced in the database. Several normal forms have been identified .The most important and widely used normal forms are.
- First Normal Form (1 NF)
- Second Normal Form (2 NF)
- Third Normal Form (3 NF)
- Fourth Normal Form (4NF)
- Fifth Normal Form (5NF)
- Boyce-Codd Normal Form(BCNF)
First Normal Form (1 NF)
- Eliminate duplicative columns from the same table.
- Create separate tables for each group of related data and identify each row with a unique column or set of columns (the primary key).
Second Normal Form (2 NF)
- Meet all the requirements of the first normal form.
- Remove subsets of data that apply to multiple rows of a table and place them in separate tables.
- Create relationships between these new tables and their predecessors through the use of foreign keys
Third Normal Form (3 NF)
- Meet all the requirements of the second normal form.
- Remove columns that are not dependent upon the primary key.
Fourth Normal Form (4 NF)
- Meet all the requirements of the third normal form.
- A relation is in 4NF if it has no multi-valued dependencies.
Remember, these normalization guidelines are cumulative. For a database to be in 2NF, it must first fulfill all the criteria of a 1NF database.
Fifth Normal Form (5 NF)
- One advantage of fifth normal form is that certain redundancies can be eliminated.
- Fifth normal form does not differ from fourth normal form unless there exists a symmetric constraint.
- Fifth normal form deals with cases where information can be reconstructed from smaller pieces of information that can be maintained with less redundancy. 2 NF, 3 NF, and 4 NF normal forms also serve this purpose, but 5 NF normal forms generalize to cases not covered by the others.
Boyce-Codd Normal Form (BCNF)
- BCNF is based on the concept of a determinant.
- A determinant is any attribute (simple or composite) on which some other attribute is fully functionally dependent.
- A relation is in BCNF is, and only if, every determinant is a candidate key.