A transaction is one or more QUEL statements that are processed as a single database action. The effects of a transaction on the database become permanent and visible to other users when the transaction is committed.

Your application program can abort (reverse the effects) of some or all of the statements within a multi-query transaction (MQT). The ability to execute groups of statements as a single transaction, and to selectively abort transactions, enables you to ensure that your applications preserve the consistency of the data in the database.

The DBMS Server insures that simultaneously executing transactions do not interfere with each other–this is called "concurrency control." For more information about concurrency issues, see Deadlock: Detection, Avoidance, and Handling.