Domain 

You can use domain definitions to define and name domains for table columns.

Each domain definition has a name that is unique within the overall database system. If a domain has been defined without an owner being entered, the database system searches for the domain in the catalog parts in the following order:

...

       1.      Catalog part of the current owner

       2.      Catalog part of the database administrator who created the current user

       3.      Catalog part of the database system administrator

See also:

SQL Reference Manual, Domain Name

SQL Tutorial, Domains