Thursday, September 24, 2015

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, unlike a natural (or business) key which is derived from application data.

There are at least two definitions of a surrogate:

Surrogate (1) – Hall, Owlett and Todd (1976)
    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. [1]
Surrogate (2) – Wieringa and De Jonge (1991)
    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.

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