Domains are aliases for built-in data types, including precision and scale values where applicable.
Domains, also called user-defined data types, allow columns throughout a database to be defined automatically on the same data type, with the same NULL or NOT NULL condition. This encourages consistency throughout the database. Domain names are case-insensitive. Sybase IQ returns an error if you attempt to create a domain with the same name as an existing domain except for case.