What if the system fails?

What if more than one user is concurrently accessing the same data?

A transaction is a collection of operations that performs a single logical function in a database application.
e.g., deposit, withdrawal, transfer between accounts

Transaction-management component ensures that the database remains in a consistent (correct) state despite system failures (e.g., power failures and operating system crashes) and transaction failures.

e.g., system crash cannot wipe out“committed”transactions

Concurrency-control manager controls the interaction among the concurrent transactions, to ensure the consistency of the database.

e.g., two users accessing the same bank account cannot“corrupt”the system or withdraw more than allowed