Third Normal Form (3NF)

Posted By on October 7, 2014


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Second Normal Form (2NF)
Closure of a Set of Functional Dependencies

Third Normal Form:

For a relation to be in Third Normal Form, it must be in Second Normal form and the following must satisfy:

  • No non-prime attribute is transitively dependent on prime key attribute
  • For any non-trivial functional dependency, X → A, then either
  • X is a superkey or,
  • A is prime attribute.
[Image: Relation not in 3NF]

We find that in above depicted Student_detail relation, Stu_ID is key and only prime key attribute. We find that City can be identified by Stu_ID as well as Zip itself. Neither Zip is a superkey nor City is a prime attribute. Additionally, Stu_ID → Zip → City, so there exists transitive dependency.

[Image: Relation in 3NF]

We broke the relation as above depicted two relations to bring it into 3NF.

Boyce-Codd Normal Form:

BCNF is an extension of Third Normal Form in strict way. BCNF states that

  • For any non-trivial functional dependency, X → A, then X must be a super-key.

In the above depicted picture, Stu_ID is super-key in Student_Detail relation and Zip is super-key in ZipCodes relation. So,

Stu_ID → Stu_Name, Zip

And

Zip → City

Confirms, that both relations are in BCNF.

 

Second Normal Form (2NF)
Closure of a Set of Functional Dependencies

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Posted by Akash Kurup

Founder and C.E.O, World4Engineers Educationist and Entrepreneur by passion. Orator and blogger by hobby

Website: http://world4engineers.com