Normal Forms in Relational Databases

First Normal Form (1NF)

A relation is in first normal form if every attribute in that relation is single-valued.

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Second Normal Form (2NF)

A relation is in Second Normal Form (2NF) if it is in First Normal Form and every non-primary-key attribute is fully functionally dependent on the primary key.

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Third Normal Form (3NF)

A relation is in the third normal form if there is no transitive dependency for non-prime attributes and it is in the second normal form, as well.

A relation is in 3NF if at least one of the following two conditions holds in every non-trivial function dependency X –> Y.

  • X is a super key, or
  • Y is a prime attribute (that is, each element of Y is part of some candidate key)

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Boyce-Codd Normal Form (BCNF)

For BCNF the relation should satisfy the below conditions:

  • The relation should be in the 3rd Normal Form, and
  • X should be a superkey for every functional dependency (FD) X−>Y in a given relation.

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Fourth Normal Form (4NF)

A relation R is in 4NF if and only if the following conditions are satisfied:

  • It should be in the Boyce-Codd Normal Form (BCNF), and
  • no table should has a Multi-valued Dependency.

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Fifth Normal Form (5NF)

A relation R is in 5NF if and only if it satisfies the following conditions:

  • It is already in 4NF, and
  • tt cannot be further non-loss decomposed (join dependency).

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