Database Management System Questions and Answers

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.