Atomicity

Atomicity requires that each transaction is "all or nothing": if one part of the transaction fails, the entire transaction fails, and the database state is left unchanged. An atomic system must guarantee atomicity in each and every situation, including power failures, errors, and crashes.

Consistency

The consistency property ensures that any transaction will bring the database from one valid state to another. Any data written to the database must be valid according to all defined rules, including but not limited to constraints, cascades, triggers, and any combination thereof.

Isolation

The isolation property ensures that the concurrent execution of transactions results in a system state that could have been obtained if transactions are executed serially, i.e. one after the other. Each transaction has to execute in total isolation i.e. if T1 and T2 are being executed concurrently then both of them should remain unaware of each other's presence

Durability

Durability means that once a transaction has been committed, it will remain so, even in the event of power loss, crashes, or errors. In a relational database, for instance, once a group of SQL statements execute, the results need to be stored permanently (even if the database crashes immediately thereafter).