> dearly love to find is a tool that takes this information about
> classes and their relationships, from any input, whether that input is
> an XML file, a schema for a DB, or a suite of compilation units/source
> code files for whatever language, and creates all the other forms it
> requires (ideally letting me create the relevant UML diagram and
> create the works from that.  But I guess that is too utopian fo rthis
> industry.

To avoid making this an N-squared problem, the usual solution is to pick 
one core representation and write 2(N-1) conversions between it and the 
others; you can then run two of those back-to-back to convert between 
forms other than the core. Some implementations of this kind of system 
have used XML as the core representation; others have used databases or 
other programming structures.

The hard part is automating the construction of those conversion 
routines. Websearch for the phrase "data binding" will find some tools 
that have been written for that purpose, not all XML-related. The 
problem is that the quirks of each possible representation tend to make 
producing a _complete_ interoperable conversion environment more than 
slightly painful; it may wind up needing enough manual assistance that 
it's simpler just to hand-code the conversions in the first place.

Have fun...