GATE PYQ

Database Management System

Q91.
Consider a relation R( A, B, C, D, E ) with the following three functional dependencies.AB \rightarrow C;BC \rightarrow D; C \rightarrow E; The number of superkeys in the relation R is .

Q92.
Immunity of the external schemas (or application programs) to changes in the conceptual scheme is referred to as:

Q93.
Consider the following statements S1 and S2 about the relational data model: S1: A relation scheme can have at most one foreign key. S2: A foreign key in a relation scheme R cannot be used to refer to tuples of R. Which one of the following choices is correct?

Q94.
Which one of the options given below refers to the degree (or arity) of a relation in relational database systems?

Q95.
Consider a selection of the form \sigma_{A\leq 100} (r), where r is a relation with 1000 tuples. Assume that the attribute values for A among the tuples are uniformly distributed in the interval [0, 500]. Which one of the following options is the best estimate of the number of tuples returned by the given selection query ?

Q96.
Consider the join of a relation R with a relation S. If R has m tuples and S has n tuples then the maximum and minimum sizes of the join respectively are

Q97.
Let R1(\underline{A},B,(C)) and R2(\underline{D},E) be two relation schema, where the primary keys are shown underlined, and let C be a foreign key in R1 referring to R2 . Suppose there is no violation of the above referential integrity constraint in the corresponding relation instances r1 and r2 . Which one of the following relational algebra expressions would necessarily produce an empty relation?

Q98.
Given two union compatible relations R_1(A, B) and R_2 (C, D), what is the result of the operation R_1 \Join_{ A = C \wedge B = D} R_2?

Q99.
Let r and s be two relations over the relation schemes R and S respectively, and let A be an attribute in R. Then the relational algebra expression \sigma _{A=a}(r\Join s) is always equal to :

Q100.
Consider the relation R(P,Q,S,T,X,Y,Z,W) with the following functional dependencies. PQ\rightarrow X;\quad P\rightarrow YX;\quad Q\rightarrow Y; \quad Y\rightarrow ZW Consider the decomposition of the relation R into the constituent relations according to the following two decomposition schemes. D1:\quad R=[(P,QS,T);\;(P,T,X);\;(Q,Y);\;(Y,Z,W)] D2:\quad R=[(P,Q,S);\;(T,X);\;(Q,Y);\;(Y,Z,W)] Which one of the following options is correct?