Explain the concept of a database transaction.

A database transaction is a unit of work performed within a database management system against a database.

In more detail, a database transaction is a sequence of one or more operations executed as a single logical unit of work. These operations typically include reading from the database (a 'select' operation), writing (an 'insert' or 'update' operation), or deleting data. A transaction is a fundamental concept in database systems, and it is designed to ensure data integrity and consistency.

The concept of a transaction is based on four key properties, often referred to as the ACID properties: Atomicity, Consistency, Isolation, and Durability. Atomicity means that a transaction is treated as a single, indivisible unit of work, which either succeeds completely or fails completely. If any part of the transaction fails, the entire transaction fails and the database is left unchanged. Consistency ensures that a transaction brings the database from one valid state to another. Isolation ensures that concurrent execution of transactions leaves the database in the same state that would have been obtained if the transactions were executed sequentially. Durability guarantees that once a transaction has been committed, it will remain committed even in the case of a system failure.

Transactions are controlled using two operations: 'commit' and 'rollback'. When a transaction is committed, the changes made in the database are saved and become visible to other transactions. If a transaction is rolled back, all changes made in the transaction are discarded, and the database is returned to the state it was in before the transaction began.

In summary, a database transaction is a powerful tool that allows multiple changes to a database to be bundled together into a single operation, ensuring data integrity and consistency. It is a fundamental concept in all major database systems and is crucial for maintaining the reliability and robustness of database applications.