Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. 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. The Surrogate definition relates to a data model rather than a storage model and is used throughout this article. 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.

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