Technical Interview Questions and Answers :: Virtusa
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USED TO CONVERT HIERACHICAL STRUCTURE TO THE FLAT STRUCTURE. IT IS USED TO JOIN A TABLE ITSELF AS LIKE IF THAT IS THE SECOND TABLE
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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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The domain of an attribute must include only atomic (simple, indivisible) values.
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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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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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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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A relation schema R is in BCNF if it is in 3NF and satisfies an additional constraint that for every FD X -> A, X must be a candidate key.
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A relation schema R is said to be in 4NF if for every Multivalued dependency X ->-> Y that holds over R, one of following is true
> X is subset or equal to (or) XY = R.
> X is a super key.
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A Relation schema R is said to be 5NF if for every join dependency {R1, R2, ..., Rn} that holds R, one the following is true
> Ri = R for some i.
> The join dependency is implied by the set of FD, over R in which the left side is key of R.