Question :

What is the Difference between BCNF and 4NF in DBMS.

Subject

Database Management System

Standard

Computer Science Engineering

Views

808

Asked By

Seema

Knowledge
Answer / Solution

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 :

  • It must be in Boyce Codd Normal Form (BCNF).
  • It should have no multi-valued dependency.
Knowledge
Answer / Solution

The difference between BCNF and 4NF in DBMS are following.

BCNF 4NF
A relation in BCNF must also be in 3NF. A relation in 4NF must also be in Boyce Codd Normal Form (BCNF).
A relation in BCNF may have multi-valued dependency. A relation in 4NF must not have any multi-valued dependency.
A relation in BCNF may or may not be in 4NF. A relation in 4NF is always in BCNF.
BCNF is less stronger in comparison to 4NF. 4NF is more stronger in comparison to BCNF.
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 .
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.
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.
Dependency preserving is hard to achieve in BCNF. Dependency preserving is more hard to achieve in 4NF as compared to BCNF.
In real world database designing, generally 3NF or BCNF is preferred. In real world database designing, generally 4NF is not preferred by database designer.
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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