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Written by Administrator
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Thursday, 09 July 2009 08:54 |
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Page 7 of 17 NormalizationNormalization is the process of efficiently organizing data in a database. There are two goals of the normalization process: eliminating redundant data (for example, storing the same data in more than one table) and ensuring data dependencies make sense (only storing related data in a table). Both of these are worthy goals as they reduce the amount of space a database consumes and ensure that data is logically stored.
Normalizing data in the database consists of three steps: - Eliminating any repeating groups by putting them into separate tables.
- Eliminating redundant data (occurring in more than one table).
- Eliminating attributes in a table that are not dependent on the primary key of that table.
Normal FormsIn practical applications, you'll often see 1NF, 2NF, and 3NF along with the occasional 4NF. Fifth normal form is very rarely seen.
First Normal Form (1NF) It sets the very basic rules: - Eliminate duplicative columns from the same table.
- Create separate tables for each group of related data and identify the primary key.
Second Normal Form (2NF) It addresses the concept of removing duplicative data: - Meet all the requirements of the first normal form.
- Remove subsets of data that apply to multiple rows of a table and place them in separate tables.
- Create relationships between these new tables and their predecessors through the use of foreign keys.
Third Normal Form (3NF)
- Meet all the requirements of the second normal form.
- Remove columns that are not dependent upon the primary key.
Fourth Normal Form (4NF)
- Meet all the requirements of the third normal form.
- A relation is in 4NF if it has no multi-valued dependencies.
Remember, these normalization guidelines are cumulative. For a database to be in 2NF, it must first fulfill all the criteria of a 1NF database.
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Last Updated on Friday, 28 August 2009 05:04 |
