What does ACID stand for in databases?

• A. Atomicity, Consistency, Integration, Durability
• B. Atomicity, Correctness, Isolation, Durability
• C. Atomicity, Consistency, Isolation, Availability
• D. Atomicity, Consistency, Isolation, Durability

Answer: (D)

ACID refers to four guarantees that ensure database transactions are reliable and predictable: atomicity, consistency, isolation, and durability. Atomicity means a transaction is all or nothing—it either completes completely or has no effect at all. Consistency ensures that a transaction moves the database from one valid state to another, preserving all defined rules and constraints. Isolation protects against interference between concurrent transactions, so each one appears to run in isolation as if others aren’t happening. Durability guarantees that once a transaction has been committed, its effects survive any subsequent failures, typically thanks to persistent logging and stable storage.

For example, in transferring funds from one account to another, atomicity ensures you don’t end up with a debit without the corresponding credit. Consistency keeps the total money balance within allowed constraints, isolation prevents other transactions from seeing intermediate states, and durability ensures the transfer is permanent after it’s committed, even if a crash occurs afterward.

Other terms like integration, correctness, or availability aren’t the standard descriptors used for ACID. The correct expansion is atomicity, consistency, isolation, durability.