Exam-style question
Try this first
Explain what properties a relation must have to be in third normal form. Include the role of the key and explain what must not occur between non-key attributes.
Model answer
What a good answer should say
- A relation in third normal form must already be in second normal form.
- Each non-key attribute must depend on the whole key, and no non-key attribute may depend on another non-key attribute.
- Therefore, non-key attributes depend directly on the key rather than through another non-key attribute.
- The relation should also have a key that identifies each record.
Explanation
Why this works
A complete answer identifies both requirements: the relation is already in second normal form, and it has no transitive dependency between non-key attributes. For example, if DepartmentName depends on DepartmentID and DepartmentID is linked to EmployeeID, DepartmentName should not be stored as an attribute that indirectly depends on EmployeeID in the same relation.
Common mistake
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