Database Reference
In-Depth Information
normal form than third normal form. It is designed to cover those anomalies that may arise
when there is more than one candidate key in some set of data requirements. Boyce/Codd
normal form states, essentially, that there must be no functional dependencies between can-
didate keys.
BCNF is often considered an extension or variation of the 3NF because it addresses situ-
ations where multiple, overlapping candidate keys exist. The following conditions must
hold true:
1. A table must be in 3NF.
2. All the candidate keys are composite keys made up of more than one column.
3. The relation must have two or more candidate keys.
4. The candidate keys each have duplicate columns, that is, at least one column in common
with another candidate key.
Let us take an example, the relation shown in following figure. The relation is in third nor-
mal form (assuming supplier names are unique), but it still have some redundant data.
