Surrogate Key

A surrogate key in a database is a unique identifier for either an entity in the modeled world or an object in the database. The surrogate key is not derived from application data.

Two definitions of a surrogate appear in the literature:

Surrogate (1)

This definition is based on that given by Hall, Owlett and Todd (1976). Here a surrogate represents an entity in the outside world. The surrogate is internally generated by the system but is nevertheless visible to the user or application.

Surrogate (2)

This definition is based on that given by Wieringa and De Jonge (1991). Here a surrogate represents an object in the database itself. The surrogate is internally generated by the system and is invisible to the user or application.