By definition, referential integrity is a property of data which, when satisfied, requires any field in a table that is declared a foreign key can contain only values from a parent table's primary key.
In legacy R:BASE versions, data integrity and referential integrity had to be enforced through rules and programming. They are now a part of the database structure called constraints and are automatically enforced when defined. The constraints that can be defined include:
•Primary Key
•Foreign Key
•Unique Key
•Unique Index
•Not NULL
