Mark works as a Database Administrator for Techworld Inc. He wants to remove the columns from a
table that are not dependent on the
primary key. Which of the following normal forms will help him accomplish the task?
A.
4 NF
B.
6 NF
C.
5 NF
D.
3 NF
Explanation:
Third normal form (3NF) is used in database normalization. A table is in 3NF if and only if the relation
S (table) is in second normal form (2NF)
and every non-prime attribute of S is non-transitively dependent on every key of S.
Answer A is incorrect. Fourth normal form (4NF) is a normal form used in database normalization.
Introduced by Ronald Fagin in 1977,
4NF is the next level of normalization after Boyce-Codd normal form (BCNF). Whereas the second,
third, and Boyce-Codd normal forms are
concerned with functional dependencies, 4NF is concerned with a more general type of dependency
known as a multivalued dependency.
Symbolically, it can be represented as follows:
If A -> > B|C, then A -> B and A -> C
Here, A, B, and C are attributes.
Answer C is incorrect. 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 5NF if and only if every join dependency in it is implied by the candidate keys.
Answer B is incorrect. Sixth normal form (6NF) is used in database normalization. A relation (table)
is in sixth normal form if and only if it
satisfies no nontrivial join dependencies at all. A join dependency is trivial if and only if at least one
of the projections involved is taken over
the set of all attributes of the relation (table) concerned.