Difference between BCNF and 4NF in DBMS
Last Updated :
14 Jul, 2020
1. Boyce-Codd Normal Form (BCNF) :
Any relation is said to be in the BCNF if and only if it satisfies the following condition :
- For every Functional Dependency (FD) X->Y, X is SuperKey in given relation.
2. 4th Normal Form (4NF) :
Any relation is said to be in the fourth normal form when it satisfies the following conditions :
A multi-valued dependency is said to occur when there are two attributes in a table which depend on a third attribute but are independent of each other. In order to denote a multi-valued dependency, “->->” this sign is used.
Difference between BCNF and 4NF :
S.No. |
BCNF |
4NF |
1
|
A relation in BCNF must also be in 3NF.
|
A relation in 4NF must also be in Boyce Codd Normal Form (BCNF).
|
2
|
A relation in BCNF may have multi-valued dependency.
|
<A relation in 4NF must not have any multi-valued dependency.
|
3
|
A relation in BCNF may or may not be in 4NF.
|
A relation in 4NF is always in BCNF.
|
4
|
BCNF is less stronger in comparison to 4NF.
|
4NF is more stronger in comparison to BCNF.
|
5
|
If a relation is in BCNF then it will have more redundancy as compared to 4NF.
|
If a relation is in 4NF then it will have less redundancy as compared to BCNF .
|
6
|
If a relation is in BCNF then all redundancy based on functional dependency has been removed.
|
If a relation is in 4NF then all redundancy based on functional dependency as well as multi-valued dependency has been removed.
|
7
|
For a relation, number of tables in BCNF is less than or equal to number of tables in 4NF.
|
For a relation, number of tables in 4NF is greater than or equal to number of tables in BCNF.
|
8
|
Dependency preserving is hard to achieve in BCNF.
|
Dependency preserving is more hard to achieve in 4NF as compared to BCNF.
|
9
|
In real world database designing, generally 3NF or BCNF is preferred.
|
In real world database designing, generally 4NF is not preferred by database designer.
|
10
|
A relation in BCNF may contain multi-valued as well as join dependency.
|
A relation in 4NF may only contain join dependency.
|
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