ACID Properties (Transaction):

• Atomicity: Transaction is all-or-nothing indivisible. Either all operations done or none upon failure, via log/undo. Example: Transfer money debit and credit both or none.

• Consistency: Transaction transforms database from one consistent state (satisfying integrity constraints, invariants) to another. If constraints violated, abort.

• Isolation: Concurrent transactions appear isolated, intermediate states hidden, final result as if serial. Via concurrency control (2PL, MVCC). Prevents dirty/read phenomena.

• Durability: Once committed, results persist despite failures (via write-ahead logging, stable storage, checkpoints). Committed data not lost on crash.

Together ensure reliable transaction processing despite concurrency and failures. Example: Banking transaction respects ACID: atomic transfer, consistent balance >=0, isolated from others, durable after commit.