>Enforcing RI at the business tier and enacting RI at the data tier maybe? I know where you are going but am having trouble phrasing it as well.

Not sure if I follow.

The main point is that VFP mixes different things using the same technology. There are 1:n relations which are plain technical issues (simply the fact that a customers phone numbers have to be in a separate tables as VFPs tables don't have "collection" fields is one example). There are other 1:n relations that are business issues. A customer with many invoices for instance.

Invoices and customers are two different business entities. Phone numbers belong to customers just like the customer's name. Therefore phone numbers and customers are one entity.

Relations between entities need to be enforced by the business logic. Relationships within one entity are technical issues (that typically only occur in relational systems). Therefore, they need to be handled in the data tier, so we can swap the data tier our easily.

Markus