SET RELATION TO... is just a convenient way to automatically move the record pointer in table B when you move the record pointer in table A ... think of it as a SEEK() command that automatically seeks in the related table for the expression used the SET RELATION TO command.

So no, in my opinion, you should not try to use SET RELATION TO to restrict data inserts or updates or deletes - I'm not even sure how you could.

Take a look at CREATE TRIGGER - that is a type of stored procedure that is stored in the database container, that you set to execute when data is about to be changed. I do not use database containers for things like triggers - I would use the backend database such as SQL or ORACLE - so I cannot help you much more on how to use database container triggers.