Mumbai University > Computer Engineering > Sem 4 > Database Management System

Marks: 5 M

Year: Dec 2014

Atomicity

• Atomicity refers to the ability of the database to guarantee that either all of the tasks of a transaction are performed or none of them are. Database modifications must follow an all or nothing rule.
• Each transaction is said to be atomic if when one part of the transaction fails, the entire transaction fails.
• There must be no state in database where the transaction is left partially completed. States should be defined either before the execution of the transaction or after the execution/abortion/failure of the transaction.

Consistency

• The consistency property ensures that the database remains in a consistent state before the start of the transaction and after the transaction is over.
• There must not be any possibility that some data is incorrectly affected by the execution of transaction.
• If the database was in a consistent state before the execution of the transaction, it must remain in consistent state after the execution of the transaction.

Isolation

• Isolation refers to the requirement that other operations cannot access or see the data in an intermediate state during a transaction.
• In a database system where more than one transaction are being executed simultaneously and in parallel, the property of isolation states that all the transactions will be carried out and executed as if it is the only transaction in the system.
• This constraint is required to maintain the performance as well as the consistency between transactions in a database.
• Thus, each transaction is unaware of another transactions executing concurrently in the system.

Durability

• Durability refers to the guarantee that once the user has been notified of success, the transaction will persist, and not be undone.
• All updates made on the database will persist even if the system fails and restarts. If a transaction writes or updates some data in database and commits that data will always be there in the database. If the transaction commits but data is not written on the disk and the system fails, that data will be updated once the s- - This means it will survive system failure, and that the database system has checked the integrity constraints and won't need to abort the transaction.