Boyce-Code Normal Form


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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.
  1. The candidate keys are composite.
  2. There are more than one candidate keys in the relation.
  3. There are some common attributes in the relation
Professor Code Department Head of Dept. Percent Time
P1 Physics Ghosh 50
P1 Mathematics Krishnan 50
P2 Chemistry Rao 25
P2 Physics Ghosh 75
P3 Mathematics Krishnan 100

Consider, as an example, the above relation. It is assumed that:

  1. A professor can work in more than one department
  2. The percentage of the time he spends in each department is given.
  3. Each department has only one Head of Department.
  4. 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
P1 Physics 50
P1 Mathematics 50
P2 Chemistry 25
P2 Physics 75
P3 Mathematics 100


Department Head of Dept.
Physics Ghosh
Mathematics Krishnan
Chemistry Rao

See the dependency diagrams for these new relations.







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