Computing A2 Normalisation

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  • Created by: Beth Dion
  • Created on: 27-06-13 13:48

What is Normalisation?

Normalisation is a technique used for designing relational database tables to minimize duplication of information and in so doing, to safeguard the database against logical or structural problems.

It usually provides rules that help

1.    Organise the data efficiently

2.    Eliminate redundant data

3.    Ensure only related data is stored in a table

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What are Normal Forms?

Good rules that have been developed that allow a database to be designed with different levels of efficiency. These are normal forms and are numbered from 0 to 5. The short hand for these are 0NF, 1NF, 2NF, 3NF, 4NF, 5NF.

The designer chooses what form he needs depending on what kind of database is going to be developed.

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What are First Normal Forms?

For a database to be in 1st Normal Form, the database must meet a set of specific rules. 1.    There are no columns with repeated or similar data

2.    Each data item cannot be broken down any further 3.    Each row is unique 4.    Each field has an unique name   Atomic is the work used to describe an item of data that cannot be broken down any further. e.g; an ID number, NI Number, Stock Code

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What is a Second Normal Form?

Second Normal Forms have an extra rule. The rules are

  • Non Key attributes must depend on every part of the primary key
  • The table must already be in first normal form

Any table that is already in 1NF and has a simple primary key is automatically in second normal form as well.

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What is Third Normal Form?

For a database to be in third normal form, the following rules must be met:

  • Already in 2NF
  • There are no non-key attributes that depend on another non-key attribute
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Benefits of Normalisation

  • the database does not have redundant data. It is smaller in size so less money is spent on storage.
  • Because there is less data to look through, it is much faster to run a query on data.
  • Because there is no data duplication, there is better data integrity and less risk of mistake.
  • There is no data duplication so there is less chance of storing two or more different copies of the data
  • Once change can be made which can be instantly be cascaded across any related records.
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Problems of Normalisation

  • Must be careful with trying to make data atomic. Just because you can split data, it isnt always necessary.
  • You can end up with more tables that an unnormalised database
  • The more tables and the more complec the database, the slower queries can be to run
  • It is necessary to assign more relationships to interact with larger numbers of tables
  • With more tables, Queries can be more complex to make.  
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Problems of Normalisation

  • Must be careful with trying to make data atomic. Just because you can split data, it isnt always necessary.
  • You can end up with more tables that an unnormalised database
  • The more tables and the more complec the database, the slower queries can be to run
  • It is necessary to assign more relationships to interact with larger numbers of tables
  • With more tables, Queries can be more complex to make.  
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