Answer Posted / sudhakar

Normalization is the process of efficiently organizing data
in a database. There are two goals of the normalization
process: eliminating redundant data (for example, storing
the same data in more than one table) and ensuring data
dependencies make sense (only storing related data in a
table). 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

The database community has developed a series of guidelines
for ensuring that databases are normalized. These are
referred to as normal forms and are numbered from one (the
lowest form of normalization, referred to as first normal
form or 1NF) through five (fifth normal form or 5NF). In
practical applications, you'll often see 1NF, 2NF, and 3NF
along with the occasional 4NF. Fifth normal form is very
rarely seen and won't be discussed in this article.

Before we begin our discussion of the normal forms, it's
important to point out that they are guidelines and
guidelines only. Occasionally, it becomes necessary to
stray from them to meet practical business requirements.
However, when variations take place, it's extremely
important to evaluate any possible ramifications they could
have on your system and account for possible
inconsistencies. That said, let's explore the normal forms.

First Normal Form (1NF)

First normal form (1NF) sets the very basic rules for an
organized database:
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 (2NF)

Second normal form (2NF) further addresses the concept of
removing duplicative data:
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 (3NF)

Third normal form (3NF) goes one large step further:
Meet all the requirements of the second normal form.
Remove columns that are not dependent upon the primary key.

Fourth Normal Form (4NF)

Finally, fourth normal form (4NF) has one additional
requirement:
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.

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