Normalising Databases

Normalising: getting rid of redundant data
if there is redundant data:

• takes up too much space
• if one needs to be edited than all will required to be edited
• creates maintainence problems

Normalisation process is theorectically by progressional decomposing design into a sequence of normal forms - first, second and third.

First Normal Form (1NF):

• deals with the removal of repeating attributes across horizontal rows abnd ensures each field holds single data items.
• each field stores single data
• no multiple data items within individual fields and no fields are repeated

Second Normal Form (2NF)

• removes redundant data within verticle columns ro fields
• all tables must be in first normal form
• every non-key attribute is funtionally dependant on the table's primary key - but not unique (primary key defines the attribute + identifies the non key attribute - functionallt dependant) 
• e.g date of birth, address and phone number are functionaly dependant on student ID

Third Normal Form (3NF)

• removes furyher redundant data within vertical columns or fields
• all tables must be in second normal form
• every non-key attribute is functionally dependant only on teh table's primary key and not on any other attributes of the table.
• e.g. Kmart Layby! -> Layby no. -> phone number, suburb, surname -> functionally dependant on customer details