Zend PHP 5.3 Certification Exam
Databases and SQL
Functions and Arrays
Object Oriented Programming
Data Format & Types
Strings and Patterns
Web Features 1
Which of the following recovers the committed transaction updates against any kind of system failure?
Answer option C is correct.
Durability recovers the committed transaction updates against any kind of system failure. It is guaranteed that once a user notified for successful transaction, the transaction will not be lost. The changes in transaction's data will survive system failure, and that all integrity constraints have been satisfied; therefore, there is no need to reverse the transaction. Many database systems implement durability by writing transactions into a transaction log that can be reprocessed to recreate the system state right before any later failure.
Answer option D is incorrect. Atomicity means the property of DBMS to guarantee that either all of the tasks in a given transaction are performed or none of those is performed. A transaction is an atomic unit of work. This means that in order to be in a transaction, a group of activities should succeed or all of them should fail. If a transaction is interrupted, all the previous steps within that transaction are undone.
Answer option A is incorrect. Consistency refers to the behavior of data after a transaction is completed. Whether a transaction commits or rolls back, it must leave the data in a consistent state. For example, when money is withdrawn from an ATM, the amount of money deducted from the balance must be equal to the money that the cardholder has received. If a transaction consisted of an attempt to delete a record referenced by another, each of the following mechanisms would maintain consistency:
Abort the transaction, rolling back to the consistent, prior state;
Delete all records that reference the deleted record; or, Remove the relevant fields in all records that point to the deleted record.
Answer option B is incorrect. A transaction must be performed such that it is unaffected by any other part of the system. This means that the data a transaction accesses cannot be affected by any other part of the system until the transaction is completed. This property is directly related to the consistency property, as the violation of this property may leave data in an inconsistent state.
© 2013 Zend PHP Certification Exam