Foreign keys that you can create in the Application Builder prevent deletion of a record in the lookup table if a reference to it is stored in the lookup field.
For example, when a foreign key is created on the “Customer” field for “Invoices” item, user won’t be able to delete a customer in “Customers” catalog if a reference to it is stored in “Invoices”.
The soft delete attribute of the lookup item must be set to false (see Item Editor Dialog ) for the lookup field to appear in the Foreign Keys Dialog