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Re: Thoughts about path and intermediaries

From: Jean-Jacques Moreau <moreau@crf.canon.fr>
Date: Mon, 19 Feb 2001 16:14:47 +0100
Message-ID: <3A913867.88D7F7F6@crf.canon.fr>
To: Noah_Mendelsohn@lotus.com
CC: Martin Gudgin <marting@develop.com>, Henrik Frystyk Nielsen <frystyk@microsoft.com>, XML Protocol Comments <xml-dist-app@w3.org>
I would claim that identifying actors via binding-specific URIs is a
degenerate case of the more general form of identification you propose.

Indeed, let:

   * httpUri be the URI for the HTTP binding;
   * queueUri be the URI for the queue binding;
   * actorUri be the URI for the actor itself (let's call the actor Y).

A sender X may reach Y through two different routes:

   * X -> httpUri -> actorUri -> Y
   * X -> queueUri -> actorUri -> Y

In the degenerate case where Y is accessible only through HTTP, there is only
one route:

   * X -> httpUri -> actorUri -> Y

It is then probably an overkill to use two URIs to identify the same target;
hence the reason for generally dropping one of them:

   * X -> httpUri -> Y

Now the question becomes: what does the actorUri look like? It is a URN?


Noah_Mendelsohn@lotus.com wrote:

> At the risk of somewhat muddying the waters, this reminds me of a
> distinction that I have been drawing in my own mind, and which may or may
> not in fact be a good one: I tend to think of the identities of actors as
> being in principle distinct from the binding specific URIs that one might
> actually use to transmit a message.
> One way to motivate this is to consider a situation in which two
> applications happen to be connected by two parallel bindings, perhaps one
> HTTP and one a queuing system.  I think I would expect to see in the actor
> attribute a URI that identified the receiving application or code (I think
> we have a term for this but I forget what it is) in the abstract.  So,
> this header might be directed to the transaction manager inside my
> application (not the transaction manager has reached by HTTP as distinct
> from the transaction manager as reached by the queuing system).  As I have
> previously suggested, there may be a useful role for some notion of path
> or partial order expressed at this level: which headers must be processed
> ahead of which others.
> Now, I would assume that the SOAP implementation at the sending end would
> be aware of the multiple delivery strategies available from the two
> bindings, and would in fact actually send the message along the "physical"
> path by directing it to the appropriate binding-dependent URI.  In
> general, I would assume that headers would be generated and actors
> identified far in advance of any knowledge of the actual interconnection
> technology used to deliver the message.  This is particularly true in
> scenarios were messages to travel across organizational boundaries: I
> certainly do not want you to know if I have changed my internal delivery
> technologies.
> So in summary, the notion of path that interests me at the moment, if any,
> is at the abstract level of headers and actors.  In any case, I would
> welcome discussion of my presumption that actors are, at least in the
> general case, named at a level that is potentially independent of
> particular bindings or physical end points.  Of course, nothing would
> prevent one from basing an actor name on a binding-specific URI in
> situations where that is in fact a sensible strategy.  Comments?
> ------------------------------------------------------------------------
> Noah Mendelsohn                                    Voice: 1-617-693-4036
> Lotus Development Corp.                            Fax: 1-617-693-8676
> One Rogers Street
> Cambridge, MA 02142
> ------------------------------------------------------------------------
Received on Monday, 19 February 2001 10:15:48 UTC

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