Domain Types

1. Attributes may have the same domain, e.g. cname and employee-name.
2. It is not as clear whether bname and cname domains ought to be distinct.

3. At the implementation level, they are both character strings.

4. At the conceptual level, we do not expect customers to have the same names as branches, in general.

5. Strong typing of domains allows us to test for values inserted, and whether queries make sense.