Database Normalisation Process
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Explains 3rd Form Normalisation with an example.
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Database Normalisation Process
- 2. Normalisation Normalisation is the process of identifying and eliminating data anomalies and redundancies, thereby improving data integrity and efficiency in a relational database. This process is designed to remove repeated data and improve database design.
- 3. Normalisation What does that mean?
- 4. Normalisation Basically we are making a database where – 1. Records are unique – So two people named John Smith won’t break the database 2. We aren’t doubling up data – So if we update something we only need to do it in one place 3. We can add data without creating empty fields 4. We can delete data without losing other data we would like to keep
- 5. What happens in Normalisation? During normalisation a relation is split into a number of smaller tables suitable for implementation in a relational database.
- 6. Microsoft Xbox 1S $399 Sony PlayStation 4 $509 $148 Lets look at an example. EB Games is a store that sells a variety of consoles for example – Here are EB games sales records. Cust Name Item Shipping Address Supplier Supplier Phone Price John Smith XBox One 35 Palm St, Melville Microsoft (08) BUY- XBOX $399 Roger Banks Playstation 4 47 Campus Rd, Murdoch Sony (08) BUY- SONY $509 Evan Wilson XBox One, PS Vita 38 Rock Av, Coogee Wholesale Toll Free $547 John Smith Playstation 4 47 Campus Rd, Murdoch Sony (08) BUY- SONY $509
- 7. 1stNormal Form 1. Each cell to be Single valued 2. Entries in a column are same type 3. Rows uniquely identified – Add Unique ID, or Add more columns to make unique Cust Name Item Shipping Address Supplier Supplier Phone Price John Smith XBox One 35 Palm St, Melville Microsoft (08) BUY- XBOX $399 Roger Banks Playstation 4 47 Campus Rd, Murdoch Sony (08) BUY- SONY $509 Evan Wilson XBox One, PS Vita 38 Rock Av, Coogee Wholesale Toll Free $547 John Smith Playstation 4 47 Campus Rd, Murdoch Sony (08) BUY- SONY $509
- 8. 1stNormal Form 1. Each cell to be Single valued 2. Entries in a column are same type 3. Rows uniquely identified – Add Unique ID, or Add more columns to make unique Cust Name Item Shipping Address Supplier Supplier Phone Price John Smith XBox One 35 Palm St, Melville Microsoft (08) BUY- XBOX $399 Roger Banks Playstation 4 47 Campus Rd, Murdoch Sony (08) BUY- SONY $509 Evan Wilson XBox One, PS Vita 38 Rock Av, Coogee Wholesale Toll Free $547 John Smith Playstation 4 47 Campus Rd, Murdoch Sony (08) BUY- SONY $509 2. Not Same Type1. Not a Single Value 3. Row uniquely Identified *doesn’t account for people with the same name*
- 9. So here is that table Normalised to the 1st Normal Form. The colour is just to highlight the changes. Primary Key Cust ID Cust Name Item Shipping Address Supplier Supplier Phone Price 1000 John Smith XBox One 35 Palm St, Melville Microsoft (08) BUY- XBOX $399 1001 Roger Banks Playstation 4 47 Campus Rd, Murdoch Sony (08) BUY- SONY $509 1002 Evan Wilson XBox One 38 Rock Av, Coogee Microsoft (08) BUY- XBOX $399 1002 Evan Wilson PS Vita 38 Rock Av, Coogee Sony (08) BUY- SONY $148 1003 John Smith Playstation 4 47 Campus Rd, Murdoch Sony (08) BUY- SONY $509 1. So to get to single values Evan Wilson’s entry was separated to two entries one for the XBox and one for the Vita. 2. Wholesale and Toll Free were removed and replaced with proper values that reflect the information expected. 3. A Primary Key (Cust ID) was added to make sure each row is uniquely identified. So we now see clearly that the two John Smiths are two different customers.
- 10. 2nd Normal Form 1. All attributes (Non-Key Columns) dependant on the key. So which attributes are not dependant on Cust ID in previous table? Primary Key Cust ID Cust Name Item Shipping Address Supplier Supplier Phone Price 1000 John Smith XBox One 35 Palm St, Melville Microsoft (08) BUY- XBOX $399 1001 Roger Banks Playstation 4 47 Campus Rd, Murdoch Sony (08) BUY- SONY $509 1002 Evan Wilson XBox One 38 Rock Av, Coogee Microsoft (08) BUY- XBOX $399 1002 Evan Wilson PS Vita 38 Rock Av, Coogee Sony (08) BUY- SONY $148 1003 John Smith Playstation 4 47 Campus Rd, Murdoch Sony (08) BUY- SONY $509
- 11. 2nd Normal Form 1. All attributes (Non-Key Columns) dependant on the key. So which attributes are not dependant on Cust ID in previous table? Primary Key Cust ID Cust Name Item Shipping Address Supplier Supplier Phone Price 1000 John Smith XBox One 35 Palm St, Melville Microsoft (08) BUY- XBOX $399 1001 Roger Banks Playstation 4 47 Campus Rd, Murdoch Sony (08) BUY- SONY $509 1002 Evan Wilson XBox One 38 Rock Av, Coogee Microsoft (08) BUY- XBOX $399 1002 Evan Wilson PS Vita 38 Rock Av, Coogee Sony (08) BUY- SONY $148 1003 John Smith Playstation 4 47 Campus Rd, Murdoch Sony (08) BUY- SONY $509 The Supplier, Supplier Phone and Price and not dependant on the key. They are independent to the person buying the console. Microsoft is the supplier of XBox regardless of who is buying it. So we will take these items out into their own table.
- 12. I have used the name of the item as a primary key to make it a little clearer what is going on. You probably wouldn’t do this in real life, there would be a stock number associated with these items. Primary Key Primary Key Cust ID Cust Name Shipping Address Stock ID Supplier Supplier Phone Price 1000 John Smith 35 Palm St, Melville XBox One Microsoft (08) BUY- XBOX $399 1001 Roger Banks 47 Campus Rd, Murdoch PlayStation 4 Sony (08) BUY- SONY $509 1002 Evan Wilson 38 Rock Av, Coogee PS Vita Sony (08) BUY- SONY $148 1003 John Smith 47 Campus Rd, Murdoch So we have the non-dependant data out but now we can’t see who bought what so we add table called a junction table to join them together.
- 13. I have used the name of the item as a primary key to make it a little clearer what is going on. You probably wouldn’t do this in real life, there would be a stock number associated with these items. Primary Key Primary Key Cust ID Cust Name Shipping Address Stock ID Supplier Supplier Phone Price 1000 John Smith 35 Palm St, Melville XBox One Microsoft (08) BUY- XBOX $399 1001 Roger Banks 47 Campus Rd, Murdoch PlayStation 4 Sony (08) BUY- SONY $509 1002 Evan Wilson 38 Rock Av, Coogee PS Vita Sony (08) BUY- SONY $148 1003 John Smith 47 Campus Rd, Murdoch So we have the non-dependant data out but now we can’t see who bought what so we add table called a junction table to join them together. Primary Key Primary Key Cust ID Stock ID 1000 XBox One 1001 PlayStation 4 1002 XBox One 1002 PS Vita 1003 PlayStation 4
- 14. 3rd Normal Form 1. All fields (columns) can be determined only but the key in the table and no other column. What filed can be determined by a column other than the key in our example? Primary Key Primary Key Cust ID Cust Name Shipping Address Stock ID Supplier Supplier Phone Price 1000 John Smith 35 Palm St, Melville XBox One Microsoft (08) BUY- XBOX $399 1001 Roger Banks 47 Campus Rd, Murdoch PlayStation 4 Sony (08) BUY- SONY $509 1002 Evan Wilson 38 Rock Av, Coogee PS Vita Sony (08) BUY- SONY $148 1003 John Smith 47 Campus Rd, Murdoch Primary Key Primary Key Cust ID Stock ID 1000 XBox One 1001 PlayStation 4 1002 XBox One 1002 PS Vita 1003 PlayStation 4
- 15. 3rd Normal Form 1. All fields (columns) can be determined only but the key in the table and no other column. In our example the Supplier Phone is dependent on the supplier. If we left this and the supplier changed their number we would need to change it in multiple places. Primary Key Primary Key Cust ID Cust Name Shipping Address Stock ID Supplier Supplier Phone Price 1000 John Smith 35 Palm St, Melville XBox One Microsoft (08) BUY- XBOX $399 1001 Roger Banks 47 Campus Rd, Murdoch PlayStation 4 Sony (08) BUY- SONY $509 1002 Evan Wilson 38 Rock Av, Coogee PS Vita Sony (08) BUY- SONY $148 1003 John Smith 47 Campus Rd, Murdoch Primary Key Primary Key Cust ID Stock ID 1000 XBox One 1001 PlayStation 4 1002 XBox One 1002 PS Vita 1003 PlayStation 4 So we pull out the Supplier making it a Primary Key in it’s own table and a Foreign key in Stock Table. Which will means you can only add suppliers from the Supplier Table in the Stock Table.
- 16. 3rd Normal Form 1. All fields (columns) can be determined only but the key in the table and no other column. So we pull out the Supplier making it a Primary Key in it’s own table and a Foreign key in Stock Table. Which will means you can only add suppliers from the Supplier Table in the Stock Table. Primary Key Primary Key Cust ID Cust Name Shipping Address Stock ID Supplier Price 1000 John Smith 35 Palm St, Melville XBox One Microsoft $399 1001 Roger Banks 47 Campus Rd, Murdoch PlayStation 4 Sony $509 1002 Evan Wilson 38 Rock Av, Coogee PS Vita Sony $148 1003 John Smith 47 Campus Rd, Murdoch Primary Key Primary Key Cust ID Stock ID 1000 XBox One 1001 PlayStation 4 1002 XBox One 1002 PS Vita 1003 PlayStation 4 Primary Key Supplier Supplier Phone Microsoft (08) BUY- XBOX Sony (08) BUY- SONY And we are done! Yes there is 4th Normal form but we don’t need to know about that.