A database management system is a piece of software that provides services for accessing a database, while maintaining all the required features of the data. The major functions of DBMS are

A transaction is a sequence of database operations that represents a logical unit of work and that accesses a database and transforms it from one state to another. A transaction can update or delete a record, modify a set of records, etc., when the DBMS does a commit the changes made by the transaction are made permanent. If you do not want to make the changes permanent you can rollback the transaction and the database will remain in its original state.

Concurrency control is the database management activity of coordinating the actions of database manipulation processes that operate concurrently and access shared data thus interfering with one another. The goal of an ideal concurrency management mechanism is to allow concurrency while maintaining the consistency of the shared data.

The recovery management system in a database ensures that the aborted or failed transactions create no adverse effects on the database or the other transactions. Recovery mechanisms in a DBMS make sure that the database is returned to a consistent state after a transaction fails or aborts. Recovery is very much related to concurrency in the sense that, the more the concurrency the more is the chance that an aborted transaction can affect many other transactions.