To create a domain, select the Object / Design function or click on the 
toolbar button from the main menu or from a domain list to change to design mode.
The same attributes are used to describe a domain as were used for a column: Code, Data Type, Length, Decimals, and Default.
As with the table constraint, you can formulate a logical expression in the Constraint box. When a table is defined, the expression can contain column names from the table; when a domain is defined, however, a position indicator with the format [ ] (left bracket, right bracket) is used instead. The position indicator represents the column to which the domain definition is assigned. The constraint within the domain definition cannot refer to more than one column.
Create the domain using the Object / Save function while specifying the domain name.
You can also begin by transferring an existing domain definition to an empty definition window using Object / Copy, modify it as desired, and then save it under a different domain name using the Object / Save function.
You cannot modify domains subsequently; i.e., the Object / Save function is not available in design mode for an existing domain.