## JNU 2018-1 PhD CS

 Question 1
Recursively enumerable languages are not closed under
 A concatenation B complement C union D homomorphism
Question 1 Explanation:
Recursively enumerable languages are closed under concatenation,union,homomorphism but not closed under complementation
 Question 2
Let L be a language that can be recognized by a finite automaton. The language LR consisting of reverse of the elements of L is a
 A regular language B context-free language C context-sensitive language D recursive language
Question 2 Explanation:
The language that can be recognized by a finite automata is called regular language.And regular language is closed under reversal
 Question 3

Consider the following context-free grammar:

S → XY, X → aX | bX | a, Y → Ya | Yb | a

A string generated by this grammar has
 A at least one b B no consecutive a’s or b’s C at least two a’s D last symbol as a E None of the above
Question 3 Explanation:
Let's check option wise,
Option a is false because string “aa” is generated by the given grammar which does not contain b’s.
Option b is false because string “aa” is generated by the given grammar which contains consecutive a’s.
Option d is false because string “aba” contains the last symbol as ‘a’ but not generated by the grammar.
Option c is also false because string “aba” contains two a’s but not generated by the grammar.
 Question 4
The basic logic of pumping lemma can be considered as a good example of
 A recursion B iteration C pigeonhole principle D divide-and-conquer
Question 4 Explanation:
The pigeonhole principle states that if you have fewer holes than objects then at least one holes has multiple objects in it.It states that put one object in each hole and then there must exist at least one hole which must have more than one object.
In the theory of formal languages in computability theory, a pumping lemma or pumping argument states that, for a particular language to be a member of a language class, any sufficiently long string in the language contains a section, or sections, that can be removed, or repeated any number of times, with the resulting string remaining in that language. The proofs of these lemmas typically require counting arguments such as the pigeonhole principle. Hence, the logic of pumping lemma is a good example of the pigeonhole principle.
 Question 5
Which of the following scheduling algorithms is non-preemptive?
 A Round-robin B First in, first out C Multilevel queue scheduling D Multilevel queue scheduling with feedback
Question 5 Explanation:
First-in-first-out scheduling algorithms are non preemptive scheduling algorithms because in this the process is served according to first come first served manner.
 Question 6
The part of machine level instruction, which tells central processor what has to be done, is
 A address B locator C operation code D flip-flop
Question 6 Explanation:
An opcode (abbreviated from operation code), also known as instruction machine code, is the portion of a machine language instruction that specifies the operation to be performed. Beside the opcode itself, most instructions also specify the data they will process, in the form of operands.
 Question 7
Which module gives control of the CPU to the process selected by the short-term scheduler?
 A Dispatcher B Interrupt C Scheduler D None of the above
Question 7 Explanation:
The process is selected by the scheduler and then it is the dispatcher who gives the control of the CPU to the process selected by the scheduler
 Question 8
Which of the following is the locality of reference used in OS?
 A Memory is the locality in the system B Cache memory is local memory C Main memory is local memory D Control moves from one locality to another during the execution
Question 8 Explanation:
Cache operation is based on the principle of locality of reference. There are two ways with which data or instruction is fetched from main memory and get stored in cache memory. These two ways are the following:
->Spatial locality
->Temporal locality
 Question 9
The database does not have the component
 A user data B metadata C reports D indexes
Question 9 Explanation:
Component of database includes indexes, data dictionary, metadata, description. But reports are not components. It is generated by user according to their need.
 Question 10
Data duplication is affected by normalization in the way it
 A eliminates B reduces C increases D does not affect at all
Question 10 Explanation:
Database normalization is the process of structuring the relational database in accordance with the series of so called normal forms in order to reduce data redundancy and improve data integrity.
 Question 11
There are no multivalued attributes and also no partial dependencies in a relation. The relation is in
 A first normal form B second normal form C third normal form D fourth normal form
Question 11 Explanation:
A relation is in 2NF or second normal form if there is no partial dependencies in a relation.
 Question 12
Relational algebra is related to
 A metalanguage B data definition language C procedural query language D non-procedural query language
Question 12 Explanation:
Relational algebra is procedural query language.
 Question 13
Which of the following operations can be applied on arrays?
 A Updation B Addition C Deletion D All of the above
Question 13 Explanation:
An array is collection of items stored at contiguous memory locations. The idea is to store multiple items of same type together. This makes it easier to calculate the position of each element by simply adding an offset to a base value, i.e., the memory location of the first element of the array
All of the above given operations can be applied on arrays.
 Question 14
The binary search of n data elements needs at most the comparisons
 A log2(n) - 1 B log2(n)+ 1 C log2(n) - 2 D log2(n) - 4
 Question 15
Which is not true for a B-tree of order m?
 A Leaf nodes must be at the same level B All the key values within a node must be in ascending order C All non-leaf nodes must have at least m/2 children D A non-leaf node with (n-1) keys must have n numbers of children
Question 15 Explanation:
Option c is false because if non leaf node is root node then it can have atleast two children
There are 15 questions to complete.

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