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# Technical Interview Questions and Answers :: DBMS

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What is Normalization? Write different NFs?
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It is a process of analyzing the given relation schemas based on their Functional Dependencies (FDs) and primary key to achieve the properties
> Minimizing redundancy
> Minimizing insertion, deletion and update anomalies.

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What is Functional Dependency?
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A Functional dependency is denoted by X->Y between two sets of attributes X and Y that are subsets of R specifies a constraint on the possible tuple that can form a relation state r of R. The constraint is for any two tuples t1 and t2 in r if t1[X] = t2[X] then they have t1[Y] = t2[Y]. This means the value of X component of a tuple uniquely determines the value of component Y.

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When is a functional dependency F said to be minimal?
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> Every dependency in F has a single attribute for its right-hand side.
> We cannot replace any dependency X A in F-> with a dependency Y A where Y-> is a proper subset of X and still have a set of dependency that is equivalent to F.
> We cannot remove any dependency from F and still have set of dependency that is equivalent to F.

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What is Multivalued dependency?
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Multivalued dependency denoted by X -> Y specified on relation schema R, where X and Y are both subsets of R, specifies the following constraint on any relation r of R: if two tuples t1 and t2 exist in r such that t1[X] = t2[X] then t3 and t4 should also exist in r with the following properties
> 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]
where [Z = (R-(X U Y)) ]

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What is Lossless join property?
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It guarantees that the spurious tuple generation does not occur with respect to relation schemas after decomposition.

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What is 1 NF (Normal Form)?
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The domain of an attribute must include only atomic (simple, indivisible) values.

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What is Fully Functional dependency?
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It is based on the concept of full functional dependency. A functional dependency X -> Y is full functional dependency if removal of any attribute A from X means that the dependency does not hold any more.

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What is 2NF?
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A relation schema R is in 2NF if it is in 1NF and every non-prime attribute A in R is fully functionally dependent on primary key.

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What is 3NF?
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A relation schema R is in 3NF if it is in 2NF and for every FD X -> A either of the following is true
> X is a Super-key of R.
> A is a prime attribute of R.
In other words, if every non prime attribute is non-transitively dependent on primary key.

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What is BCNF (Boyce-Codd Normal Form)?
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