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Domain

19 October, 2015 - 15:29

A domain is the original sets of atomic values used to model data. By atomic, we mean that each value in the domain is indivisible as far as the relational model is concerned. For example:

  • The domain of Marital status has a set of possibilities: Married, Single, Divorced
  • The domain of day Shift has the set of all possible days : {Mon, Tue, Wed…}.
  • The domain of Salary is the set of all floating-point numbers greater than 0 and less than 200,000.
  • The domain of First Name is the set of character strings that represents names of people.

In summary, a Domain is a set of acceptable values that a column is allowed to contain. This is based on various properties and the data type for the column. We will discuss data types in another chapter.