Can you explain what is meant by the data consistency principle?

The principle of data consistency means that the data in the system is always in a correct, expected state after operations are performed. In the context of databases, this means that any transactions transition the database from one valid state to another, adhering to all constraints, rules, and data integrity.

For example, if there is a rule in the database that the sum of accounts cannot be negative, then after a withdrawal operation, this rule must still hold — the database should not end up in a state with a negative balance.

In programming, this helps ensure that data will not be corrupted or contradictory after changes.