You've answered your own question.
Quote:
(property*,mapping+,(class-cache|collection-cache|jcs-class-cache|jcs-collection-cache)*)(property*,mapping+,(class-cache|collection-cache|jcs-class-cache|jcs-collection-cache)*)
The 'mapping+' restriction is what's hampering your efforts.
I would try (bear in mind that I have not tried any of these myself), in order of preference
1) Programatically configuring the session
2) mapping an simple arbitrary object from each of the databases (say table foo with column bar), but stick to the XML
3) using a properties file (no DTD validation)
BTW
what happens if you put an empty mapping element in ?