5NF - Definition - Database

Q.  What is 5NF?
- Published on 26 Aug 15

a. The database should be in 3NF and all tables can have only one primary key.
b. There should be no cyclic dependencies in a composite key.
c. All attributes within the entity should depend solely on the entity's unique identifier.
d. Tables cannot have multi - valued dependencies on a Primary Key.

ANSWER: There should be no cyclic dependencies in a composite key.


  • Nirja Shah   -Posted on 03 Nov 15
    - Fifth normal form (5NF), also known as project-join normal form (PJ/NF) is a level of database normalization designed to reduce redundancy in relational databases recording multi-valued facts by isolating semantically related multiple relationships.

    - A table is said to be in the 5NF if and only if every non-trivial join dependency in it is implied by the candidate keys.

    - A join dependency *{A, B, … Z} on R is implied by the candidate key(s) of R if and only if each of A, B, …, Z is a superkey for R.

    - The fifth normal form was first described by Ronald Fagin in his 1979 conference paper Normal forms and relational database operators.

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