schema management for a document pipeline: request for comment

["DuCharme, Bob (LNG)" <bob.ducharme@lexisnexis.com>]

It's reasonable to assume that a document moving through a pipeline of
processes will conform to a slightly different schema after each stage. For
example, a checkIn date-time stamp attribute may not be in the arriving
document, but process two may require that it's in process one's output.

How do you manage this collection of what are essentially variations on the
same schema? I have a more detailed statement of the problem and a proposal
for a solution at http://www.snee.com/xml/schemaStages.html. The problem and
solution apply equally to W3C and RELAX NG schemas. 

I'd like to hear any comments and suggestions. For example, my examples are
pretty simple; can anyone think of a reason that it might not scale well?

thanks,

Bob DuCharme          www.snee.com/bob           <bob@  
snee.com>  "The elements be kind to thee, and make thy
spirits all of comfort!" Anthony and Cleopatra, III ii