data domain

Article summary

In database theory, a data domain is the collection of values that a data element may contain. The rule for determining the domain boundary may be as simple as a data type with an enumerated list of values. For example, a database table that has information about people, with one record per person, might have a "marital status" column. This column might be declared as a string data type, and allowed to have one of two known code values: "M" for married, "S" for single, and NULL for records where marital status is unknown or not applicable. The data domain for the marital status column is: "M", "S". In a normalized data model, the reference domain is typically specified in a reference table. Following the previous example, a Marital Status 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. 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 that the values must be greater than zero.…

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