What is Normalisation (or Normalization)?

Why do database guys go on about normalization?

What is it? How does it help?

Does it apply to anything outside of databases?

Normalization is basically to design a database schema such that duplicate and redundant data is avoided. If some piece of data is duplicated several places in the database, there is the risk that it is updated in one place but not the other, leading to data corruption.

Normalization also defined as removal of data redundancy or elements that we don't need.

Some say Normalization also causes performance issues.Indeed it does.

Referential Integrity
Data to be protected by laws of database. 
If I normalize, I will maximize referential integrity.

Getting to fully normalize creates stages
Ist Normal Form or Ist NF
DB to achieve INF means no repeating elements
Elements tend to repeate in groups so no repeating groups

2nd NF No partial dependency on
  part of primary key (PK)

3rd NF no non key attributes
dependent on another non key attributes

There is also 4th and 5th but industry don't imply.
Industry ok with 3rdNF

Is it important? Yes, it is very important. By having a database with normalization errors, you open the risk of getting invalid or corrupt data into the database. Since data "lives forever" it is very hard to get rid of corrupt data when first it has entered the database.

Related articles

• Normalisation - A Technique to Design a Database System
• Normalisation. can anyone help me?