Relational databases handle business rules and policies at a very granular level, with strict policies about commitment (that is, making a change to the database permanent). For example, consider an inventory database that tracks three parts that are always used together. When one part is pulled from inventory, the other two must also be pulled. If one of the three parts isn’t available, none of the parts should be pulled—all three parts must be available before the database makes any commitment. A relational database won’t commit for one part until it knows it can commit for all three. This multifaceted commitment capability is called atomicity. Atomicity is the key to keeping data accurate in the database and ensuring that it is compliant with the rules, regulations, and policies of the business.
Four crucial properties define relational database transactions: atomicity, consistency, isolation, and durability—typically referred to as ACID.
Atomicity defines all the elements that make up a complete database transaction.
Consistency defines the rules for maintaining data points in a correct state after a transaction.
Isolation keeps the effect of a transaction invisible to others until it is committed, to avoid confusion.
Durability ensures that data changes become permanent once the transaction is committed.
