Business rules define how data should be managed and used within a system. For example, a business rule might require that each user have a unique name, or that all orders must be paid for before being shipped. Other rules might limit the order amount to the customer’s account balance, or stipulate that an order can only be canceled before it is shipped. Additionally, it might be necessary to check a product’s availability before adding it to an order.

There are several approaches to implementing these business rules. They can be coded directly into the system using dedicated methods, functions, or classes. Unit tests can also be used to verify compliance with these rules, for example, by ensuring the uniqueness of usernames. Finally, business rules can be integrated into the database using constraints such as data typing, uniqueness of values, or foreign keys, as well as triggers and transactions to guarantee data consistency.