1. Anomalies can occur in relations in 3NF if there is a composite key in which part of that key has a determinant which is not itself a candidate key.


2. This can be expressed as R(A,B,C), C--->A where:
   
   
   
   • The relation R contains attributes A, B and C.
   
   
   • A and B form a candidate key.
   
   
   • C is the determinant for A (A is functionally dependent on C).
   
   
   • C is not part of any key.
   
   
   
   


3. Anomalies can also occur where a relation contains several candidate keys where:
   
   
   
   • The keys contain more than one attribute (they are composite keys).
   
   
   • An attribute is common to more than one key.
   
   
   
   

Example to understand BCNF:-

Take the following table:

Note that no two buildings on any of the university campuses have the same name, thus ROOM/BLDG----->CAMPUS. As the determinant is not a candidate key this table is NOT in Boyce-Codd normal form.

This table should be decomposed into the following relations:

R1(course, class, room/bldg, time)

R2(room/bldg, campus)