States of Transactions
A transaction is started as a program. From the Start state as the transaction is scheduled by the CPU it moves to the Execute state, however, in case of any system error at that point it may also be moved into the Abort state. During the execution, transaction changes the data values and database moves to an inconsistent state. On successful completion of transaction it moves to the Commit state where the durability feature of transaction ensures that the changes will not be lost. In case of any error, the transaction goes to Rollback state where all the changes made by the transaction are undone. Thus, after commit or rollback database is back into consistent state. In case a transaction has been rolled back, it is started as a new transaction.