restrict content to values out of a xml file

hi,

when checking a xml-file (with xsd-file),
is there a way to restrict the content of an element to values that are
defined in another xml file, for example i have the element "name" in the
xml file i want to check, and the only names that are allowed are defined
in another xml-file in the element "allowed_names".
should be some kind of enumeration thing, with the difference that i dont't
want to type in the allowed names in the xsd file, but write them in an
extern xml file.
can anyone help???

thanx in advance,
nadine