Boyce-Codd Normal Form(BCNF)

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A table is in Boyce-Codd normal form (BCNF) if and only if it is in 3NF and every determinant is a candidate key.

  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:





























campus course class time room/bldg

East


English 101


1


8:00-9:00


212 AYE


East


English 101


2


10:00-11:00


305 RFK


West


English 101


3


8:00-9:00


102 PPR


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)


























course class time room/bldg

English 101


1


8:00-9:00


212 AYE


English 101


2


10:00-11:00


305 RFK


English 101


3


8:00-9:00


102 PPR


R2(room/bldg, campus)




















campus room/bldg

East


212 AYE


East


305 RFK


West


102 PPR


 

                    

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