What are transactions? Explain the reasons for use and the properties of ACID.

A transaction is a sequence of operations on a database that is executed as a single unit. Either all operations succeed and the changes are committed, or in case of an error, all changes are rolled back to maintain data integrity.

ACID is a set of properties that guarantee reliable transactions:

• Atomicity: the transaction is either fully completed or not executed at all.
• Consistency: the transaction transforms the database from one valid state to another, adhering to all rules and constraints.
• Isolation: concurrent transactions do not affect each other as if they were executed sequentially.
• Durability: once a transaction is committed, its changes are permanent even in case of system failures.

Using transactions and ACID properties is essential to prevent errors such as partial data updates, race conditions during concurrent access, and data loss during failures.