Surrogate Key

A Surrogate Key is a database key that ...

• AKA: Synthetic Key, Entity Identifier, System-Generated Key, Database Sequence Number, Factless Key, Technical Key, Arbitrary Unique Identifier.
• See: Natural Key, Database.

---

---

References

2017

• (Wikipedia, 2017) ⇒ https://en.wikipedia.org/wiki/surrogate_key Retrieved:2017-4-17.
  • A surrogate key (or synthetic key, entity identifier, system-generated key, database sequence number, factless key, technical key, or arbitrary unique identifier) 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.

2017

• (Wikipedia, 2017) ⇒ https://en.wikipedia.org/wiki/surrogate_key#Definition Retrieved:2017-4-17.
  • There are at least two definitions of a surrogate:
    1. 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.
    2. 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. In a temporal database, however, there is a many-to-one relationship between primary keys and the surrogate. Since there may be several objects in the database corresponding to a single surrogate, we cannot use the surrogate as a primary key; another attribute is required, in addition to the surrogate, to uniquely identify each object.

    Although Hall et al. (1976) say nothing about this, othershave argued that a surrogate should have the following characteristics:

    • the value is unique system-wide, hence never reused
    • the value is system generated
    • the value is not manipulable by the user or application
    • the value contains no semantic meaning
    • the value is not visible to the user or application
    • the value is not composed of several values from different domains.

---