Domain integrity specifies that all columns in a relational database must be declared upon a defined domain. The primary unit of data in the relational data model is the data item. Such data items are said to be non-decomposable or atomic. A domain is a set of values of the same type.
Each attribute in the model should be assigned domain information which includes:
Data Type - Basic data types are integer, decimal, or character. Most data bases support variants of these plus special data types for date and time.
Length - This is the number of digits or characters in the value. For example, a value of 5 digits or 40 characters.
Date Format - The format for date values such as dd/mm/yy or mm/dd/yyyy or yy/mm/dd.
Range - The range specifies the lower and upper boundaries of the values the attribute may legally have.
Constraints - Are special restrictions on allowable values. For example, the LeavingDate for an Employee must always be greater than the HireDate for that Employee.
Null support - Indicates whether the attribute can have null values.
Default value (if any) - The value an attribute instance will have if a value is not entered.
