Database Management System Questions and Answers

Q: In a multi-user database, if two users wish to update the same record at the same time, they are prevented from doing so by

Correct answer: record lockA record lock is taken by the first transaction to reach the row, and the second must wait until it is released, so the two updates are serialised instead of overwriting each other. Passwords control who may connect, not what happens when two permitted users collide.

Q: Wait-for graph is used for

Correct answer: deadlock detectionA wait-for graph has an edge from each waiting transaction to the one holding the lock it wants; a cycle in that graph means a deadlock, which is then broken by aborting a transaction. Prevention schemes avoid deadlock in advance and need no such graph.

Q: Between DRAM and magnetic disk storage another form of memory, called ______ memory is becoming common because it is non volatile.

Correct answer: FlashFlash memory keeps its contents without power, unlike DRAM, and is far faster than a magnetic disk, so it fills the gap between the two in the storage hierarchy.

Q: ____specifies a search condition for a group or an aggregate.

Correct answer: HAVING ClauseHAVING applies its condition to groups after aggregation, which is why it can test an aggregate such as \( \text{SUM}(amount)>1000 \). WHERE is applied to individual rows before grouping and cannot see an aggregate at all.

Q: In a B-tree the number of keys in each node is ______ than the number of its children.

Correct answer: one lessIn a B-tree the keys in a node separate the ranges covered by its children, so n keys divide the range into \( n+1 \) intervals and the node has \( n+1 \) children. The number of keys is therefore one less than the number of children.

Q: Grant and revoke are _____ statements.

Correct answer: DCLGRANT and REVOKE control who may do what, so they belong to the Data Control Language. DDL defines structures, DML manipulates data, and TCL manages transactions.

Q: Shadow paging has

Correct answer: no redoShadow paging keeps the old page table until the transaction commits, and commits by switching to the new one atomically. So an aborted transaction is undone simply by discarding the new pages, and a committed one is already complete on disk - there is nothing to redo.

Q: Data items grouped together for storage purposes are called a

Correct answer: recordA record is a group of related data items stored together as a unit - the fields of one row taken as a whole. A string is a single value and a list is an arrangement, not a storage unit.

Q: Which two files are used during operation of the DBMS?

Correct answer: Data dictionary and transaction logThe data dictionary is consulted for the description of every object referred to, and the transaction log is written for every change so that recovery is possible. Both are in use continuously while the system runs.

Q: Which of the following constitutes a basic set of operations for manipulating relational data?

Correct answer: Relational algebraRelational algebra is the basic set of operations for manipulating relations - selection, projection, union, difference, product and join. Relational calculus describes results without operations, and SQL is a language built on top of the algebra.

71.

In a multi-user database, if two users wish to update the same record at the same time, they are prevented from doing so by

A.jamming
B.password
C.documentation
D.record lock

Answer: D

Correct answer: record lock

A record lock is taken by the first transaction to reach the row, and the second must wait until it is released, so the two updates are serialised instead of overwriting each other. Passwords control who may connect, not what happens when two permitted users collide.

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72.

Wait-for graph is used for

A.detecting view serializability.
B.detecting conflict serializability.
C.deadlock prevention
D.deadlock detection

Answer: D

Correct answer: deadlock detection

A wait-for graph has an edge from each waiting transaction to the one holding the lock it wants; a cycle in that graph means a deadlock, which is then broken by aborting a transaction. Prevention schemes avoid deadlock in advance and need no such graph.

Discuss in Forum

73.

Between DRAM and magnetic disk storage another form of memory, called ______ memory is becoming common because it is non volatile.

A.RAM
B.Flash
C.Hard Disk
D.Secondary

Answer: B

Correct answer: Flash

Flash memory keeps its contents without power, unlike DRAM, and is far faster than a magnetic disk, so it fills the gap between the two in the storage hierarchy.

Discuss in Forum

74.

____specifies a search condition for a group or an aggregate.

A.GROUP BY Clause
B.HAVING Clause
C.FROM Clause
D.WHERE Clause

Answer: B

Correct answer: HAVING Clause

HAVING applies its condition to groups after aggregation, which is why it can test an aggregate such as \( \text{SUM}(amount)>1000 \). WHERE is applied to individual rows before grouping and cannot see an aggregate at all.

Discuss in Forum

75.

In a B-tree the number of keys in each node is ______ than the number of its children.

A.one less
B.same
C.one more
D.half

Answer: A

Correct answer: one less

In a B-tree the keys in a node separate the ranges covered by its children, so n keys divide the range into \( n+1 \) intervals and the node has \( n+1 \) children. The number of keys is therefore one less than the number of children.

Discuss in Forum

76.

Grant and revoke are _____ statements.

A.TCL
B.DCL
C.DDL
D.DML

Answer: B

Correct answer: DCL

GRANT and REVOKE control who may do what, so they belong to the Data Control Language. DDL defines structures, DML manipulates data, and TCL manages transactions.

Discuss in Forum

77.

Shadow paging has

A.no redo
B.no undo
C.redo but no undo
D.neither redo nor undo

Answer: A

Correct answer: no redo

Shadow paging keeps the old page table until the transaction commits, and commits by switching to the new one atomically. So an aborted transaction is undone simply by discarding the new pages, and a committed one is already complete on disk - there is nothing to redo.

Discuss in Forum

78.

Data items grouped together for storage purposes are called a

A.record
B.string
C.title
D.list

Answer: A

Correct answer: record

A record is a group of related data items stored together as a unit - the fields of one row taken as a whole. A string is a single value and a list is an arrangement, not a storage unit.

Discuss in Forum

79.

Which two files are used during operation of the DBMS?

A.Query languages and utilities
B.DML and query language
C.Data dictionary and transaction log
D.Data dictionary and query language

Answer: C

Correct answer: Data dictionary and transaction log

The data dictionary is consulted for the description of every object referred to, and the transaction log is written for every change so that recovery is possible. Both are in use continuously while the system runs.

Discuss in Forum

80.

Which of the following constitutes a basic set of operations for manipulating relational data?

A.Predicate calculus
B.Relational calculus
C.Relational algebra
D.SQL

Answer: C

Correct answer: Relational algebra

Relational algebra is the basic set of operations for manipulating relations - selection, projection, union, difference, product and join. Relational calculus describes results without operations, and SQL is a language built on top of the algebra.

Discuss in Forum

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