W3C home > Mailing lists > Public > xml-dist-app@w3.org > February 2001

RE: Thoughts about path and intermediaries

From: <Noah_Mendelsohn@lotus.com>
Date: Tue, 13 Feb 2001 20:38:47 -0500
To: xml-dist-app@w3.org
Message-ID: <OFF8C76AA3.B75B1761-ON852569F3.0007938C@lotus.com>

I sort of agree with a lot of what has been written in this thread, but
it's easier for me to think about this if I can put it in my own terms for
a minute:

* Fundamentally, I think the issue is:  can you in some way express either
a total or partial order in which various headers must be processed?  This
is about at the level of mustUnderstand...if you get the order wrong,
you've got an error.

* I don't think this is directly about binding to or exposing capabilities
or compositions of the underlying transport.  If I need to "begin
transaction"  before I "update catalog", that potentially is true
regardless of transport.  Yes, there are also transport-specific
intermediaries:  different issue IMHO.

* There have been suggestions to move back to a single hop protocol,
putting all path-like notions at a higher level, and Henrik suggests (I
think) to do about what SOAP does today.  My view:  if path is application
level, then I'm not sure why SOAP-ENV:actor isn't as well.  Given that SOAP
deals at the level of naming intermediaries and targeting headers to them,
that's very close to the level at which you worry about getting to the
intermediaries in the wrong order.  It feels to me as if actor and
header-path come more or less together.

So, with the caveat that I may be completely missing something, the two
approaches that seem self-consistent to me are: (a) make the protocol
single hop, which I think means putting the attributes for actor, path, and
perhaps mustUnderstand in some higher level namespace...which we'll
probably have to design in a hurry or (b) consider expressing the full or
partial order of header processing and in that sense a path or route in
some standard way in the core protocol.

I'm not 100% sure whether I prefer to see all this in the core or layered.
Having a core point-to-point single hop protocol has always had a certain
minimalist appeal, but you can get a lot richer routing and decision making
if partial orders are visible to the routing software.

In either case, maybe it's as simple as having a mustFollow header
attribute that indicates (don't process me until you've processed (idref of
other header)?  If the attribute is missing, no order is required.  (we
have to think about cycles, etc.)

Noah Mendelsohn                                    Voice: 1-617-693-4036
Lotus Development Corp.                            Fax: 1-617-693-8676
One Rogers Street
Cambridge, MA 02142
Received on Wednesday, 14 February 2001 00:27:57 UTC

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