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By noah    Posted on 21-10-2021    89 Views    41 Downloads     fantastic, cardinal, object in english, shelf

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A surrogate key (or synthetic key, pseudokey, entity identifier, factless key, or technical 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. Definition 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. 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. The Surrogate (1) definition relates to a data model rather than a storage model and is used throughout this article. See Date (1998). An important distinction between a surrogate and a primary key depends on whether the database is a current database or a temporal database. Since a current database stores only currently valid data, there is a one-to-one correspondence between a surrogate in the modeled world and the primary key of the database. In this case the surrogate may be used as a primary key, resulting in the term surrogate key.