DS5: Proposed revision

Per discussion in the XP conference call today, here is a proposed revision
of DS5 which attempts to take a slightly more "encapsulated" view of the
scenario, focusing on what the sender is really expecting from the XP layer,
and trying to avoid any implementation details.

DS5   A sender wishes to exchange data with a receiver. Data is sent
      from the sender to the receiver, and a positive acknowledgement
      is returned to the sender indicating a successful transfer.

Note: DS5 differentiates from DS3 and DS4 in that an acknowledgement is
      semantically different from any business-level response which
      the receiver might send.  The acknowledgement only indicates a
      successful transfer of the message from one node to another.

Glen Daniels
Allaire Corp
Engineering Manager
http://www.allaire.com/
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