The ACID model is one of the oldest and most important concepts of database theory. It sets forward four goals that every database management system must strive to achieve: atomicity, consistency, isolation and durability. No database that fails to meet any of these four goals can be considered reliable. Let’s take a moment to examine each one of these characteristics in detail: Atomicity : states that database modifications must follow an “all or nothing” rule. Each transaction is said to be “atomic.” If one part of the transaction fails, the entire transaction fails. It is critical that the database management system maintain the atomic nature of transactions in spite of any DBMS, operating system or hardware failure. Consistency : states that only valid data will be written to the database. If, for some reason, a transaction is executed that violates the database’s consistency rules, the entire transaction will be rolled back and the database will be restored to a s...