1. Normalisation

2. Un-normalised Form (UNF)
Identify an entity
List all the attributes
Identify a key
ORDER
(Order Number
Order Date
Customer Number
Customer Name
Address
Post Code
Telephone Number
Item Code
Description
Unit Cost
Quantity)

3. Un-normalised Form (UNF)
Identify repeating data items

4. Un-normalised Form (UNF)
Identify repeating data items
ORDER
(Order Number
Order Date
Customer Number
Customer Name
Address
Post Code
Telephone Number
Item Code
Description
Unit Cost
Quantity)

5. First Normal Form (1NF)
Remove repeating data items to form a new entity
Take the key with you!
ORDER
(Order Number
Order Date
Customer Number
Customer Name
Address
Post Code
Telephone Number
Repeating items
Item Code
Description
Unit Cost
Quantity)

6. First Normal Form (1NF)
Remove repeating data items to form a new entity
Take the key with you!
ORDER
ORDER_ITEM
(Order Number
Order Date
Customer Number
Customer Name
Address
Post Code
Telephone Number)
Item Code
Description
Unit Cost
Quantity)

7. First Normal Form (1NF) Identify a key for the new entity
It will be a compound key
Use the original key and add to it
ORDER
ORDER_ITEM
(Order Number
Order Date
Customer Number
Customer Name
Address
Post Code
Telephone Number)
Item Code
Description
Unit Cost
Quantity)

8. First Normal Form (1NF) Identify a key for the new entity
It will be a compound key
Use the original key and add to it
Label the foreign key
Order Number is both part of the compound primary key and also a foreign key.
ORDER
ORDER_ITEM
(Order Number
Order Date
Customer Number
Customer Name
Address
Post Code
Telephone Number)
(*Order Number
Item Code
Description
Unit Cost
Quantity)

9. First Normal Form (1NF)
A data model is in 1NF if it has no multi-valued attributes
ORDER
ORDER_ITEM
(Order Number
Order Date
Customer Number
Customer Name
Address
Post Code
Telephone Number)
(*Order Number
Item Code
Description
Unit Cost
Quantity)

10. First Normal Form (1NF)

11. First Normal Form (1NF)
But what if there were lots of orders for large deluxe red widgets…?
There are still update anomalies

12. Second Normal Form (2NF)
Examine any entity with a compound key (in this case ORDER_ITEM)
See if any attributes are dependent on just one part of the compound key
These are called partial dependencies
ORDER
ORDER_ITEM
(Order Number
Order Date
Customer Number
Customer Name
Address
Post Code
Telephone Number)
(*Order Number
Item Code
Description
Unit Cost
Quantity)

13. Second Normal Form (2NF)
Order Number is part of the key
Item Code is part of the key
Description is dependent on the Item Code
Unit Cost is dependent on the Item Code
Quantity is dependent on both Order Number and Item Code.
ORDER
ORDER_ITEM
(Order Number
Order Date
Customer Number
Customer Name
Address
Post Code
Telephone Number)
(*Order Number
Item Code
Description
Unit Cost
Quantity)

14. Second Normal Form (2NF)
Description and Unit Cost are partial dependencies
They are dependent on Item Code
Remove these attributes to a new entity
Take a copy of the attribute they are dependent on
ORDER
ORDER_ITEM
(Order Number
Order Date
Customer Number
Customer Name
Address
Post Code
Telephone Number)
(*Order Number
Item Code
Description
Unit Cost
Quantity)

15. Second Normal Form (2NF)
Item Code becomes the key of the new entity
And becomes a foreign key in ORDER-ITEM
ORDER
ORDER_ITEM
ITEM
(Order Number
Order Date
Customer Number
Customer Name
Address
Post Code
Telephone Number)
(*Order Number
*Item Code
Quantity)
(Item Code
Description
Unit Cost)

16. Second Normal Form (2NF)
A data model is in 2NF if it is in 1NF and there are no partial dependencies
ORDER
ORDER_ITEM
ITEM
(Order Number
Order Date
Customer Number
Customer Name
Address
Post Code
Telephone Number)
(*Order Number
*Item Code
Quantity)
(Item Code
Description
Unit Cost)

17. Second Normal Form (2NF)
We can add an item to the Item table without it having to be on an order
We can delete an order in the Order table without deleting details of the items on the order
We can update item details once in the Item table without affecting the orders for that item in the Order-Item table

18. Second Normal Form (2NF)
But there are still update anomalies with the Order entity
ORDER
(Order Number
Order Date
Customer Number
Customer Name
Address
Post Code
Telephone Number)

19. Third Normal Form (3NF) Examine all the entities produced so far
See if there are any non-key attributes which are dependent on any other non-key attributes
These are called non-key dependencies
ORDER
ORDER_ITEM
ITEM
(Order Number
Order Date
Customer Number
Customer Name
Address
Post Code
Telephone Number)
(*Order Number
*Item Code
Quantity)
(Item Code
Description
Unit Cost)

20. Third Normal Form (3NF)
In the ORDER entity, Customer Name, Address, Post Code and Telephone Number are all dependent on Customer Number
ORDER
ORDER_ITEM
ITEM
(Order Number
Order Date
Customer Number
Customer Name
Address
Post Code
Telephone Number)
(*Order Number
*Item Code
Quantity)
(Item Code
Description
Unit Cost)

21. Third Normal Form (3NF) Remove these attributes to a new entity ORDER
ORDER_ITEM
ITEM
(Order Number
Order Date
Customer Number
Customer Name
Address
Post Code
Telephone Number)
(*Order Number
*Item Code
Quantity)
(Item Code
Description
Unit Cost)

22. Third Normal Form (3NF) Remove these attributes to a new entity
Customer Number is the key of the new entity
Leave Customer Number behind as a foreign key
ORDER
CUSTOMER
ORDER_ITEM
ITEM
(Order Number
Order Date
*Customer Number)
(Customer Number
Customer Name
Address
Post Code
Telephone Number)
(*Order Number
*Item Code
Quantity)
(Item Code
Description
Unit Cost)

23. Third Normal Form (3NF)
A data model is in 3NF if it is in 2NF and there are no non-key dependencies
ORDER
CUSTOMER
ORDER_ITEM
ITEM
(Order Number
Order Date
*Customer Number)
(Customer Number
Customer Name
Address
Post Code
Telephone Number)
(*Order Number
*Item Code
Quantity)
(Item Code
Description
Unit Cost)

24. Third Normal Form (3NF)
We can add a customer to the Customer table without the customer having to place an order
We can delete an order in the Order table without deleting details of the customer who placed the order
We can update a customer’s details once in the Customer table without affecting the orders placed by that customer in the Order table

25. Memory Aid In 3NF, each attribute is dependent on the key
the whole key
and nothing but the key