For instance, in the Orders table or in a composite table CustomersOrders we would like to disallow assigning a value to CustomerID that is not present in the Customers table. To create a referential integrity constraint relation, check the Enforce constraints check box. A relation can be a master-detail relation and a referential integrity constraint simultaneously.

By default, M-1 joins in a composite table define a referential integrity constraint. So, for example, in a composite table CustomersOrders it is not allowed to enter CustomerID that is not present in the Customers table. If you want to change this behavior, define a relation with the same joins as used in the composite table and uncheck the Enforce constraints check box.