A natural key (also known as business key or domain key) is a type of

unique key In relational database management systems, a unique key is a candidate key that is not the primary key of the relation. All the candidate keys of a relation can uniquely identify the records of the relation, but only one of them is used as the prim ...

in a

database In computing, a database is an organized collection of data stored and accessed electronically. Small databases can be stored on a file system, while large databases are hosted on computer clusters or cloud storage. The design of databases ...

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 formal sciences, the domain of discourse, also called the universe of discourse, universal set, or simply universe, is the set of entities over which certain variables of interest in some formal treatment may range. Overview The doma ...

). In the

relational model The relational model (RM) is an approach to managing data using a structure and language consistent with first-order predicate logic, first described in 1969 by English computer scientist Edgar F. Codd, where all data is represented in terms of t ...

of data, a natural key is a

superkey In the relational data model a superkey is a set of attributes that uniquely identifies each tuple of a relation. Because superkey values are unique, tuples with the same superkey value must also have the same non-key attribute values. That is, ...

and is therefore a functional determinant for all attributes in a relation. A natural key serves two complementary purposes: it provides a means of

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for data and it imposes a rule, specifically a ''uniqueness constraint'', to ensure that data remains unique within an information system. The uniqueness constraint assures uniqueness of data within a certain technical context (e.g. a set of values in a table, file or relation variable) by rejecting input of any data that would otherwise violate the constraint. This means that the user can rely on a guaranteed correspondence between facts identified by key values recorded in a system and the external domain of discourse (a single version of the truth). A natural key differs from a surrogate key which has no meaning outside the database itself and is not based on real-world observation or intended as a statement about the reality being modelled. A natural key therefore provides a certain data quality guarantee whereas a surrogate does not. It is common for elements of data to have several keys, any number of which may be natural or surrogate.

Advantages

The advantages of using a natural key to uniquely identify records in a relation include less disk space usage, the natural key is an attribute that is related to the business or the real world so in most cases, it is already being stored in the relation which saves disk space as compared to creating a new column for storing the surrogate key. Another advantage of using natural keys is that it simplifies quality of data and they are easier to relate to real life while designing the database system. They simplify the quality of data as using a natural key that is unique in the real world ensures that there cannot be multiple records with the same

primary key In the relational model of databases, a primary key is a ''specific choice'' of a ''minimal'' set of attributes ( columns) that uniquely specify a tuple ( row) in a relation ( table). Informally, a primary key is "which attributes identify a recor ...

. Comparing the database schema to a real world scenario is a huge part of designing a database schema and when a natural key is being used in the tables of the database, it makes it easy for the database engineer to engineer the database system.

Disadvantages

Usage of natural keys as unique identifiers in a table has one main disadvantage which is the change of business rules or the change of rules of the attribute in the real world. The definition of the structure of the natural key attribute might change in the future. For example if there is a table storing the information about US citizens, the

Social Security Number In the United States, a Social Security number (SSN) is a nine-digit number issued to U.S. citizens, permanent residents, and temporary (working) residents under section 205(c)(2) of the Social Security Act, codified as . The number is issued to ...

would act as the natural key, Social Security Number being the natural key might pose a problem in the future if the US government changes the structure of the Social Security Number and increases the number of digits in the SSN due to some reason. In that case, the Database Administrator will have to change the schema of the table and perhaps also update the records of the table. In other cases, this can prevent improvements of the system altogether due to too extensive effort required for the change, e.g., the inability of the knowledge management system, Confluence, to represent multiple pages with the same title.

References

{{Reflist Data modeling