• Some comments.

    The article talks about unique indexes, but formally they are alternake keys or uniquenss constraints.

    Everybody should be aware that there are situations in which surrogate keys fail to keep RI working.

    IMO RI is an physicalisation step of a data model and should not be initially modeled at all (in eg a logical model). Only when implementing you could add them to tune the database model.

    Kind Regards,

    DM Unseen AKA M. Evers