Use cases for IM's

In today's conference call, I believe I heard someone say that support
for IM's was of particularly high priority because they are needed
by CommerceOne.  Earlier email has cited CommerceOne and Ariba as
examples of IM's:

processing intermediaries. If the intermediaries were merely

and exclusively routing intermediaries, then that might be one

thing. However, I don't believe for a minute that C1 and Ariba

consider themselves as mere routers.

Do you agree that a compelling reason for providing IM functionality
is to meet the needs of compannies such as CommerceOne and Ariba?

I confess that I do not have as good an understanding as ought to of
how business processes would work in situations where a company such
as CommerceOne or Ariba (their customers, actually, if I am getting
this right) would serve as an IM.  If you agree that this is a
motivating case for IM's, I wonder if you could explain how IM's
fit into this picture.

As I understand it, these companies make software that can be used to
establish a "marketplace", in which, say, buyers and sellers, rather
than interoperating in a direct point-by-point fashion, interoperate
with the marketplace instead.  (Or maybe they do some things through
the marketplace and other things directly?)

But if I were using a marketplace, it seems to me that this would best
be modelled as a business process whose parties were me and the
marketplace.  I don't think I understand when there would be a
scenario in which party X is engaging in a business process with party
Y (e.g. X sends a request to Y and Y replies to X, or Y notifies X, or
Y solicits X and X replies to Y), but the messages between X and Y are
sent indirectly through the "marketplace" implementation acting as an
IM at the ebXML MS layer of abstraction.  Why is that the right model?

Thank you.

--
Dan