| The definition of 3rd normal form |
| It's in 2nd normal form |
| It contains no transitive dependencies (where a non-key attribute
is dependent on another non-key attribute). |
We can narrow our search down to the Employee table, which is the
only one with more than one non-key attribute. Employee name is
not dependent on either Rate category or Hourly rate, the same
applies to Rate category, but Hourly rate is dependent on Rate
category. So, as before, we remove it, placing it in it's
own table, with the attribute it was dependent on as key,
as follows:
Employee project table
Project number - primary key
Employee number - primary key
Employee table
Employee number - primary key
Employee name
Rate Category
Rate table
Rate category - primary key
Hourly rate
Project table
Project number - primary key
Project name
These tables are all now in 3rd normal form, and ready to be
implemented. There are other normal forms - Boyce-Codd normal form,
and 4th normal form, but these are very rarely used for business
applications. In most cases, tables in 3rd normal form are already
in these normal forms anyway.
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