Transaction control in a database management system (DBMS) refers to the process of managing the execution and the effects of a transaction, which is a unit of work or a logical operation that is performed on a database. Transaction control is used to ensure the integrity, the consistency, and the reliability of the data in a database, and to provide a mechanism for rollback or recovery in case of errors or failures.

Transaction control in a DBMS is implemented using a variety of techniques and technologies, such as transactions, locks, and isolation levels. A transaction is a unit of work or a logical operation that is performed on a database, and it is usually composed of one or more SQL statements or commands. A lock is a mechanism that is used to control the access or the modification of the data in a database by multiple users or processes, and it is usually implemented using various types of locks, such as shared locks, exclusive locks, and update locks. An isolation level is a property or a characteristic of a transaction that determines the level of isolation or the level of concurrency of the data in a database, and it is usually implemented using various levels of isolation, such as read uncommitted, read committed, repeatable read, and serializable.

Transaction control in a DBMS is usually implemented using the following statements or commands:

• BEGIN TRANSACTION: This statement is used to start a new transaction, and it is usually used to enclose one or more SQL statements or commands that need to be executed as a unit of work or a logical operation.
• COMMIT TRANSACTION: This statement is used to commit or save the changes or the effects of a transaction, and it is usually used to make the changes or the effects of a transaction permanent or persistent in a database.
• ROLLBACK TRANSACTION: This statement is used to rollback or undo the changes or the effects of a transaction, and it is usually used to restore the database to the state it was in before the transaction was started.
• SAVEPOINT: This statement is used to create a savepoint or a checkpoint within a transaction, and it is usually used to mark a point in a transaction where the changes or the effects can be rolled back or undone.

Transaction control in a DBMS is an essential aspect of database management, and it is used to ensure the integrity, the consistency, and the reliability of the data in a database, and to provide a mechanism for rollback or recovery in case of errors or failures. Transaction control is usually implemented using transactions, locks, and isolation levels, and it is usually implemented using the BEGIN TRANSACTION, COMMIT TRANSACTION, ROLLBACK TRANSACTION, and SAVEPOINT statements or commands.