Boyce-Code Normal Form
Boyce-Code Normal Form (BCNF)
- A relationship is said to be in BCNF if it is already in 3NF and the left hand side of every dependency is a candidate key.
- A relation which is in 3NF is almost always in BCNF. These could be same situation when a 3NF relation may not be in BCNF the following conditions are found true.
- The candidate keys are composite.
- There are more than one candidate keys in the relation.
- There are some common attributes in the relation
|Professor Code||Department||Head of Dept.||Percent Time|
Consider, as an example, the above relation. It is assumed that:
- A professor can work in more than one department
- The percentage of the time he spends in each department is given.
- Each department has only one Head of Department.
- The relation diagram for the above relation is given as the following:
The given relation is in 3NF. Observe, however, that the names of Dept. and Head of Dept. are duplicated. Further, if Professor P2 resigns, rows 3 and 4 are deleted. We lose the information that Rao is the Head of Department of Chemistry.
The normalization of the relation is done by creating a new relation for Dept. and Head of Dept. and deleting Head of Dept. form the given relation. The normalized relations are shown in the following.
|Professor Code||Department||Percent Time|
|Department||Head of Dept.|
See the dependency diagrams for these new relations.
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