XML Schema - Associate Element Name and Attribute with keys/keyrefs?

Hey all,

Is it possible to associate an element name with an attribute using a key/keyref pair?

The message I'm trying to validate would look like this:

<root>
    <global>
        <properties message-type="servermessage">
                                     ...
        </properties>
    </global>

    <servermessage>
               ...
    </servermessage>
</root>

or

<root>
    <global>
        <properties message-type="modulemessage">
                                     ...
        </properties>
    </global>

    <modulemessage>
               ...
    </modulemessage>
</root>


The general idea is that the message-type in global/properties defines what element follows it.  Right now, I have implemented a schema that uses <xs:choice> but obviously that would allow the message-type to  be modulemessage and the following element to be a servermessage element.  Any ideas on how I would go about writing a schema for what I want to do, or do I need to change how my xml is currently written to do what I want?

Thanks,
Andy