When the replica propagates data to the master, the master is not required to accept that data. Within a master/replica system, only the master has the authority to declare data official. If the master receives data that violates database rules (such as referential integrity constraints), or business rules (such as prohibiting customers from exceeding a certain credit limit), the master can reject or alter the data.
The master also has other options to bring data into conformance, such as modifying the data. For example, if a customer orders more widgets than are in stock, the master might modify the customer's order so that the customer is sent all the remaining available widgets. This way, the customer's order is not thrown out completely.
Advanced replication includes the Intelligent Transaction feature that helps application developers control the consistency of the master database. The Intelligent Transaction feature allows a transaction to validate itself in the master database and adjust its behavior to ensure the validity of the transaction.