When you add an attribute to an entity, the attribute is automatically assigned to a domain called Unknown. Each default logical data type is associated with a domain. For example, the default logical data type CHAR is associated with the String domain.
A logical data type is the property of an attribute and a domain. Therefore, you can enforce your organization's data type standards by attaching a domain to each attribute in a model. For example, if the logical model contains several United States telephone number attributes (home phone area code, business phone area code), you can add a domain named AREA CODE for which the logical data type is SMALLINT. In addition, you can attach a list of valid area codes to the domain in a validation rule (201, 609, 732, 904, and so on) and assign the local area code (609) as the default value. Finally, you can assign a display format that inserts parentheses around the area code. When you assign the AREA CODE domain to an attribute that stores telephone area code information, the attribute automatically inherits the complete set of inheritable domain properties defined in the Domain Dictionary editor.
All default and user-defined logical data types appear in the Data Type list in both the Attribute Editor and in the Domain Editor. You can also display all of the domains and logical data types assigned to attributes by selecting Entity Display from the model diagram shortcut menu, and then selecting Attribute Domain or Attribute Data Type.
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