reliable messaging

[Martin W Sachs <mwsachs@us.ibm.com>]

I would like to simplify the discussion regarding where the message is
reliably delivered to.  I recently realized that by delivering the message
to the persistent store at the upper boundary of the message service, the
message service is fulfilling its committment to deliver the message to the
application.  The middleware above the application is really a set of
services which act on behalf of the application.  The persistent store at
the upper boundary of the message store is probably the last place that the
message exists as the character string that was sent over  the wire. At
that point, the message is parsed and converted to a DOM tree or other
object structure that the application-specific code will process.  This
means that delivery of the message reliably to the application is entirely
within the scope of the message service.

As to delivery failure notification, the question is, what is the
"application" that the notification has to be reliably delivered to?  The
answer is that it is the intelligence which cares about a response and
which has to perform application-level recovery if the application-level
response does not arrive.  Delivery of the delivery failure notification
indeed involves layers of function outside the scope of the message service
specification. However, the message service specification still has the
responsibility of stating that the the delivery failure notification SHALL
be delivered to the application.  A non-normative note can explain that his
involves function that is outside the scope of the message service and that
delivery may be accomplished by any appropriate method such as API function
or by placing the notification where it can be polled by the application.

Regards,
Marty

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Martin W. Sachs
IBM T. J. Watson Research Center
P. O. B. 704
Yorktown Hts, NY 10598
914-784-7287;  IBM tie line 863-7287
Notes address:  Martin W Sachs/Watson/IBM
Internet address:  mwsachs @ us.ibm.com
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