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RE: Message reliability

From: Cutler, Roger (RogerCutler) <RogerCutler@chevrontexaco.com>
Date: Thu, 23 Oct 2003 09:31:50 -0500
Message-ID: <7FCB5A9F010AAE419A79A54B44F3718E0313280C@bocnte2k3.boc.chevrontexaco.net>
To: "He, Hao" <Hao.He@thomson.com.au>, www-ws-arch@w3.org

The explanation is fine, but isn't the definition a little odd?  It
seems to me that the highest level of certainty that sender and receiver
have the SAME understanding of the status of message delivery is when
both know it CAN'T HAPPEN AT ALL ... EVER!  I realize that there are
problems making a succinct definition because of the impossibility of
actually guaranteeing delivery in a distributed system (stated loosely),
but can't we do better than this?

You probably considered this and rejected it for some good reason, but
what is wrong with the more direct:  "Message reliability is the degree
of certainty that a message will be delivered". Or, perhaps, "Message
reliability is the degree of certainty that a message will be delivered
and that sender and recipient will both have the same understanding of
the delivery status".  It seems to me that the definition should have
something to do with what you really want, not a secondary matter that
you think might result in what you want but actually might have some
other result.  That wasn't stated very well, I know, but perhaps you get
the drift.

-----Original Message-----
From: www-ws-arch-request@w3.org [mailto:www-ws-arch-request@w3.org] On
Behalf Of He, Hao
Sent: Thursday, October 23, 2003 6:44 AM
To: 'www-ws-arch@w3.org '
Subject: Message reliability


Based on the discussion of last f2f:
http://www.w3.org/2002/ws/arch/3/09/2003-09-25-ws-arch.htm

Reliable messaging is now called message reliability.  We still need to
write text on other aspects of reliability.

Hao


 2.3.1.13 Message reliability
2.3.1.13.1 Definition
Message reliability is the degree of certainty to which both the sender
and the recipient have the same understanding of the status of message
delivery.

... skip ...

2.3.1.13.3 Explanation


The goal of message reliability is to both reduce the error frequency
for messaging and to provide sufficient information about the status of
a message delivery. Such information enables a participating agent to
make a compensating decision when errors or less than desired results
occur. High level correlation such "two-phase commit" is needed if more
than two agents are involved. Note that in a distributed system, it is
theoretically not possible to guarantee correct notification of
delivery; however, in practice, simple techniques can greatly increase
the overall confidence in the message delivery.

It is important to note that a guarantee of the delivery of messages
alone does not improve the overall reliability of a Web service due to
the "end-to-end argument."[1]  It may, however, improve the performance
of messaging, and therefore, the overall performance of a Web service.

Message reliability may be realized with a combination of message
receipt acknowledgement and correlation. In the event that a message has
not been 
properly received and acted upon, the sender may attempt a resend, or
some other compensating action at the application level.

[1]http://www.reed.com/Papers/EndtoEnd.html
Received on Thursday, 23 October 2003 10:32:15 GMT

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