I recently implemented an XMI plugin for Middlegen that is now included 
in the distribution. I designed the plugin to generate a model with 
classes and associations stereotyped as per the AndroMDA stereotypes.

It seems to me that a commonly agreed set of stereotypes and tagged-
values in the XMI model, which are preserved by all tools would go a 
long way to incorporating models into the development process. Since any 
tool would be able to generate an XMI model which could be used by any 
other tool.

For example: XDoclet > XMI > DDL (Schema)
             DDL > XMI > Java Source (XDoclet tagged)

if tools get sophisitcarted enough to merge changes into an existing 
model then we reach complete round-trip engineering, with the added 
benefit of starting where we feel comfortable, database, source code or 
UML model.

More info on my blog: <a href="http://www.behindthesite.com/blog/?
postid=2" target="_blank">Adventures in MDA</a>