When surrogate keys supplant natural keys, then domain specific referential integrity will be compromised. For example, in a customer master table, the same customer may have multiple records under separate customer IDs, even though the natural key (a combination of customer name, date of birth, and E-mail address) would be unique. To prevent compromise, the natural key of the table must NOT be supplanted: it must be preserved as a unique constraint, which is implemented as a unique index on the combination of natural-key fields.