Advanced Database Management System - Tutorials and Notes: DBMS Quiz Questions with Answers 10

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Thursday, 30 April 2020

DBMS Quiz Questions with Answers 10

Database management systems DBMS TRUE or FALSE questions with answers explained for competitive and entrance exams.


TRUE or FALSE questions in DBMS 


1. Concurrency control by timestamps is superior to that by locks if most transactions are read-only.
                   (a) TRUE                                          (b) FALSE
View Answer

Answer: TRUE
Timestamp ordering protocol is free from deadlock. Here, no transaction ever waits.
Locking protocols may lead to deadlock. Also, read locks need to be acquired in the same way for write locks. In timestamp ordering protocol, it is the time of successful transaction is used for permitting a transaction. Hence, it is not a overhead.

2. Schedules that avoid cascading rollbacks are always serializable.
                   (a) TRUE                                          (b) FALSE
View Answer

Answer: FALSE
Cascading rollback is a concept in which failure of single transaction leads to a series of transaction rollbacks. This is undesirable behavior because it undone significant amount of work.
Cascadeless schedules can safeguard a schedule from a series of transaction rollbacks. It cannot guarantee serializability.
In addition to avoidance of cascading rollbacks, at least the use of 2PL can ensure serializability.

3. Any candidate key of a relation is a super key for that relation.
                   (a) TRUE                                          (b) FALSE
View Answer

Answer: TRUE
Super key is any (any set of) attributes including redundant attributes. Candidate key is a minimal super key. That is, a candidate key is a super key with the property “no proper subset of candidate key is a super key”. In other words, candidate is a super key in which all redundant attributes are removed.

4. One weakness of triggers is that they can only be activated for insertion and update operations.
                   (a) TRUE                                          (b) FALSE
View Answer

Answer: FALSE
No. Triggers can be activated on data manipulation including insertion, deletion, and update operations.

5. The default policy for the foreign-key constraint sets the value of a foreign-key to null when the tuple of its referenced attribute gets deleted.
                   (a) TRUE                                          (b) FALSE
View Answer

Answer: FALSE
No. The referenced attribute or its value cannot be deleted without dropping the foreign key constraint or the foreign key table.

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