GATE CSE year:2017 PYQs & Answers — Page 9

Questions 81–90 of 130. Imported answers require independent review unless marked reviewed.

Consider a database that has the relation schemas EMP(EmpId, EmpName, DeptId), and DEPT(DeptName, DeptId). Note that the DeptId can be permitted to be NULL in the relation EMP. Consider the following queries on the database expressed in tuple relational calculus.

(I)

(II)

(III)

Which of the above queries are safe?

Your answerChoose one option.

(I) and (II) only

(I) and (III) only

(II) and (III) only

(I), (II) and (III)

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Let L(R) be the language represented by regular expression R. Let L(G) be the language generated by a context free grammar G. Let L(M) be the language accepted by a Turing machine M. Which of the following decision problems are undecidable?

I. Given a regular expression R and a string w, is w ∈ L(R)? II. Given a context-free grammar G, is L(G) = ∅? III. Given a context-free grammar G, is L(G) = Σ* for some alphabet Σ? IV. Given a Turing machine M and a string w, is w ∈ L(M)?

Your answerChoose one option.

I and IV only

II and III only

II, III and IV only

III and IV only

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In a database system, unique timestamps are assigned to each transaction using Lamport’s logical clock. Let

and

be the timestamps of transactions

and

respectively. Besides,

holds a lock on the resource R, and

has requested a conflicting lock on the same resource R. The following algorithm is used to prevent deadlocks in the database system assuming that a killed transaction is restarted with the same timestamp.

then

is killed

else

waits.

Assume any transaction that is not killed terminates eventually. Which of the following is TRUE about the database system that uses the above algorithm to prevent deadlocks?

Your answerChoose one option.

The database system is both deadlock-free and starvation-free.

The database system is deadlock-free, but not starvation-free.

The database system is starvation-free, but not deadlock-free.

The database system is neither deadlock-free nor starvation-free.

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The next state table of a 2-bit saturating up-counter is given below.

Q₁	Q₀	Q₁⁺	Q₀⁺
0	0	0	1
0	1	1	0
1	0	1	1
1	1	1	1

The counter is built as a synchronous sequential circuit using T flip-flops. The expressions for T₁ and T₀ are

Your answerChoose one option.

T₁ = Q₁Q₀, T₀ = Q̅₁Q̅₀

T₁ = Q̅₁Q₀, T₀ = Q̅₁ + Q̅₀

T₁ = Q₁ + Q₀, T₀ = Q̅₁ + Q̅₀

T₁ = Q̅₁Q₀, T₀ = Q₁ + Q₀

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Consider the following grammar:

stmt

if expr then expr else expr; stmt

expr

term relop term

term

number

[0-9]

where relop is a relational operator (e.g.,<, >, …), ò refers to the empty statement, and if, then, else are terminals.

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Consider the following snippet of a C program. Assume that swap(&x, &y) exchanges the contents of x and y.

int main() {

int array[] = {3, 5, 1, 4, 6, 2};

int done = 0;

int i;

while (done == 0) {

done = 1;

for (i=0; i<=4; i++) {

if (array[i] < array[i+1]) {

swap(&array[i], &array[i+1]);

done = 0;

}

for (i=5; i>=1; i--) {

if (array[i] > array[i-1]) {

swap(&array[i], &array[i-1]);

done = 0;

}

printf("%d", array[3]);

}

The output of the program is __________.

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In a RSA cryptosystem, a participant A uses two prime numbers

and

to generate her public and private keys. If the public key of A is 35, then the private key of A is __________.

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Two transactions

and

are given as

where

denotes a read operation by transaction

on a variable

and

denotes a write operation by transaction

on a variable

. The total number of conflict serializable schedules that can be formed by

and

is __________.

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The values of parameters for the Stop-and-Wait ARQ protocol are as given below: Bit rate of the transmission channel = 1 Mbps. Propagation delay from sender to receiver = 0.75 ms. Time to process a frame = 0.25 ms. Number of bytes in the information frame = 1980. Number of bytes in the acknowledge frame = 20. Number of overhead bytes in the information frame = 20.

Assume that there are no transmission errors. Then, the transmission efficiency (expressed in percentage) of the Stop-and-Wait ARQ protocol for the above parameters is __________ (correct to 2 decimal places).

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The read access times and the hit ratios for different caches in a memory hierarchy are as given below.

Cache	Read access time (in nanoseconds)	Hit ratio
I-cache	2	0.8
D-cache	2	0.9
L2-cache	8	0.9

The read access time of main memory is 90 nanoseconds. Assume that the caches use the referred-word-first read policy and the write back policy. Assume that all the caches are direct mapped caches. Assume that the dirty bit is always 0 for all the blocks in the caches. In execution of a program, 60% of memory reads are for instruction fetch and 40% are for memory operand fetch. The average read access time in nanoseconds (up to 2 decimal places) is __________.

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GATE CSE year:2017 PYQs

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