Let's run again through the example we've just done, this time
without the data tables to guide us. After all, when you're
designing a system, you usually won't have test data available at
this stage. The tables were there to show you the consequences of
storing data in unnormalized tables, but without them we can
focus on dependency issues, which is the key to database
normalization.
In the beginning, the data structure we had was as follows:
Project number
Project name
1-n Employee numbers (1-n indicates that there are many occurrences
of this field - it is a repeating group)
1-n Employee names
1-n Rate categories
1-n Hourly rates
So, to begin the normalization process, we start by moving from
zero normal form to 1st normal form.
| The definition of 1st normal form |
| there are no repeating groups |
| all the key attributes are defined |
| all attributes are dependent on the primary key |
So far, we have no keys, and there are repeating groups. So we
remove the repeating groups, and define the primary key, and are
left with the following:
Employee project table
Project number - primary key
Project name
Employee number - primary key
Employee name
Rate category
Hourly rate
This table is in 1st normal form.
Database Normalization: Part 5
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