Rules Of Data Normalisation
Let us now summarise Normalisation with the help of various clean rules. The following are the necessary rules for the Normalisation process:
1. Eliminate Repeating Groups: Make an individual relation for each set of related attributes, and give every relation a primary key.
2. Eliminate Redundant Data: If an attribute relies on only part of a multi- attribute key, remove it to an individual relation.
3. Eliminate Columns Not Dependent On Key: If attributes do not give to a description of the key, remove them to a individual relation.
4. Isolate Independent Multiple Relationships: No relation may have two or more 1:n or n:m relationships that are not directly linked.
5. Isolate Semantically Related Multiple Relationships: There may be practical constrains on information that give explanation for separating logically related many-to-many relationships.
Let's define these steps of Normalisation through an instance:
Let us make a file of all the employees in the company. In the original employee file, every employee name is pursued by any databases that the member has experience with. Some may know many, and others may not know any.
|
Emp-ID
|
Emp-Name
|
Database-Known
|
Department
|
Department- Loc
|
|
1
|
Gurpreet
Malhotra
|
Oracle,
|
A
|
N-Delhi
|
|
2
|
Faisal Khan
|
Access
|
A
|
N-Delhi
|
|
3
|
Manisha Kukreja
|
FoxPro
|
B
|
Agra
|
|
4
|
Sameer Singh
|
DB2, Oracle
|
C
|
Mumbai
|