Layering in ebXML and WSA

I for one am a bit overwhelmed by the "layers" thread.  What we need, and
which I think someone out there must have the ability to summarize, is a
paragraph or two on how messaging works in ebXML (all these acronyms such as
CPA are foreign to many of us!) and how that differs from the more typical
"stack" conception in various Web services architectures.  

I don't see any responses to Roger's
http://lists.w3.org/Archives/Public/www-ws-arch/2003Feb/0073.html
I'm especially interested in observations on his assertion that ebXML is
heavily oriented toward early-bound, "heavy" B2B/EDI operations whereas
typical Web services architectures are oriented toward late-bound and light
operations.  This sounds plausible to me, is it more or less correct?

Finally, I'd like to see suggestions for how to discuss this in the WSA
document. What properties, relationships, and constraints characterize ebXML
messaging?

Thanks for helping to direct this very informative discussion in a direction
that is more useful to the WSA WG.

Mike Champion