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Database/DBMS Interview Questions And Answers - Part XIV.


63) What Is Second (2nd) Normal Form (2NF)?

Answer: The purpose of second normal form (2NF) is to eliminate partial key dependencies. Each attribute in an entity must depend on the whole key, not just a part of it.

Definition: A relation Schema R is in 2NF if every non-prime attribute A in R is fully functionally dependent on the primary key of R.




64) What Is Third (3rd) Normal Form (3NF)?

Answer: Third Normal form also helps to eliminate redundant information by eliminating inter dependencies between non-key attributes. Before proceeding to 3NF, check that it is already in 2NF and there are no non-key attributes that depend on another non-key attribute.




65) What Is Boyce-Codd Normal Form (BCNF)? Also Define Multivalued Dependency?

Answer: A relation schema R is in Boyce-Codd Normal Form (BCNF) if whenever an FD X -> A holds in R, then X is a superkey of R.

Each normal form is strictly stronger than the previous one:
  • Every 2NF relation is in 1NF.
  • Every 3NF relation is in 2NF.
  • Every BCNF relation is in 3NF.
There exist relations that are in 3NF but not in BCNF. The goal is to have each relation in BCNF (or 3NF).


A multivalued dependency (MVD) X —>> Y specified on relation schema R, where X and Y are both subsets of R, specifies the following constraint on any relation state r of R: If two tuples t1 and t2 exist in r such that t1[X] = t2[X], then two tuples t3 and t4 should also exist in r with the following properties, where we use Z to denote

(R - (X ν Y)):
t3[X] = t4[X] = t1[X] = t2[X].
t3[Y] = t1[Y] and t4[Y] = t2[Y].
t3[Z] = t2[Z] and t4[Z] = t1[Z].

An MVD X —> Y in R is called a trivial MVD if (a) Y is a subset of X, or (b) X X —> Y = R.


ALSO CHECK THE BELOW FAQ's:

66) What is Fourth (4th) Normal Form (4NF)?
67) What is Fifth (5th) Normal Form (5NF)?
68) What Are The Lossless Inference Rules For Functional Dependencies (FD's) Or State The Armstrong's Axioms?
69) What Is Domain-Key Normal Form (DKNF)?
70) Define Transaction? Explain Different States Of Transaction?


71) Describe The ACID Properties Of A Transaction?
72) What Is Schedule & What Is The Importance Of Schedule?
73) What Do You Mean By Serializability In Transaction Processing?
74) What Are The Two Methods That Guarantee Serializability?
75) What Is Locking? What Are The Types Of Locking?

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