By using an attribute from a particular namespace which has a "global"
declaration (for example in XML Schema), you can ensure that any reference
to that attribute name will require values of the same data type. This is a
convenience to some applications, and a convenience in defining XML
structures, though not a necessity. The name may not validly be used for an
incompatible attribute. DTDs do not have a comparable facility -- they can
provide, via entities, reusable attributes, but not require that all uses be
compatible.
Jeff
