Normalisation

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)

Un-normalised Form (UNF) Identify repeating data items

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)

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)

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)

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)

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)

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)

First Normal Form (1NF)

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

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)

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)

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)

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)

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)

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

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)

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)

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)

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)

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)

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)

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

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