Data domain

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For other uses, see Data domain (disambiguation).

In data management and database analysis, a data domain refers to all the unique values which a data element may contain. The rule for determining the domain boundary may be as simple as a data type with enumerated list of values.

For example, a database table that has information about people, with one record per person, might have a "gender" column. This gender column might be declared as a string data type, and allowed to have one of two known code values: "M" for male, "F" for female -- and NULL for records where gender is unknown or not applicable (or arguably "U" for unknown as a sentinel value). The data domain for the gender column is : "M", "F".

In a normalized data model, the reference domain is typically specified in a reference table. Following the previous example, a Gender reference table would have exactly two records, one per allowed value -- excluding NULL. Reference tables are formally related to other tables in a database by the use of foreign keys.

Less simple domain boundary rules, if database-enforced, may be implemented through a check constraint or, in more complex cases, in a database trigger. For example, a column requiring positive numeric values may have a check constraint declaring the values must be greater than zero.

This definition combines the concepts of domain as an area over which control is exercised and the mathematical idea of a set of values of an independent variable for which a function is defined. See: domain (mathematics).