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Must understand mustUnderstand proposal

From: Martin Gudgin <marting@develop.com>
Date: Thu, 3 May 2001 15:49:21 +0800
Message-ID: <002801c0d3a5$9265e5f0$a5fe55cb@greyarea>
To: "XML Protocol Comments" <xml-dist-app@w3.org>
On the XML Protocol telcon today I volunteered to start discussion of an
extension Module for XMLP/SOAP. This mail serves as a kick off for
discussion of that extension.

The problem: How to make sure that all headers in a message with
mustUnderstand='1', targeted at any intermediary or the ultimate destination
have actually been processed.

Suggestion: Define an XMLP Module ( essentially an extension header, as
defined in the XMLP Requirements document[1] ) that is processed by the
ultimate destination whose semantics are; examine the XMLP/SOAP message and
ensure that; a) no header elements exist that have mustUnderstand='1' *and*
should have been processed by an intermediary b) no header elements exist
that have mustUnderstand='1' that the ultimate destination does not
understand. If either a) or b) is not true then a fault will be generated.

Observations/Open Questions:

1.    How do we make sure that the ultimate destination has processed/can
process all of the mustUnderstand='1' headers targeted at it? Or do we even
need to bother? Will knowing that intermediaries have processed their
headers, because there are no headers left in the message that are not
targeted at the ultimate destination, be enough?

2.    Do we want to deal with the 'badly written' XMLP/SOAP implementations
that claims to have processed a header but in fact has not? See mail from
Frank DeRose[2] for more detail on this question.

3.    Does an intermediary *always* remove the headers targeted at it? If
not then I think we need some way of annotating them as 'processed'.

4.    What do we do about ordering? This is an issue particularly at the
ultimate destination. What if this header is encountered before other
headers marked mustUnderstand='1'? What if it is encountered after?

5.    This header needs to be marked mustUnderstand='1' :-)

6.    This extension must be able to work by examining *only* the message
that arrives at the ultimate recipient.

7.    Is processing this at the ultimate destination enough? Or do we need
to have evaluate this at every intermediary? <gulp>

I think that'll do as a start point. Please chime in with your thoughts and
suggestions about the open questions and the semantics and we'll see how
things progress. I'd like to be able to come up with a proposal by close of
play Monday if possible.

Cheers

Martin Gudgin
DevelopMentor

[1] http://www.w3.org/TR/2001/WD-xmlp-reqs-20010319/#g350
[2] http://lists.w3.org/Archives/Public/xml-dist-app/2001May/0020.html
Received on Thursday, 3 May 2001 03:50:51 GMT

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