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A natural key (also known as business key) is a type of unique key in a database formed of attributes that exist and are used in the external world outside the database (i.e. in the business domain or domain of discourse). In the relational model of data, a natural key is a candidate key and is therefore a functional determinant for all attributes in a relation. A natural key is sometimes called domain key.
The main advantage of a natural key over a surrogate key (which has no meaning outside the database environment) is that a natural key already exists, so there is no need to add a new, artificial column to the schema. Using a natural key (when one can be identified) also simplifies data quality: It ensures that there can only be one row for a key; this single version of the truth can be verified because the natural key is based on a real-world observation.