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RE: FW: LC Comments: Web Method Feature

From: Williams, Stuart <skw@hplb.hpl.hp.com>
Date: Thu, 4 Jul 2002 09:07:54 +0100
Message-ID: <5E13A1874524D411A876006008CD059F04A06EFE@0-mail-1.hpl.hp.com>
To: "'Mark Baker'" <distobj@acm.org>
Cc: "'xml-dist-app@w3.org'" <xml-dist-app@w3.org>

Mark,

> Hey,
> 
> On Wed, Jul 03, 2002 at 06:52:28PM +0100, Williams, Stuart wrote:
> > > Where did "messaging" come from there?  I think the chameleon view is
> > > as much about messaging as the tunneling view ... at least as far as
> > > the underlying protocol permits.
> > 
> > The surface model with the REST resource state view is that of direct
access
> > and manipulation of resource state. The underlying protocols use
messaging
> > to create the illusion of shared state... but the surface model is one
of
> > state access and manipulation, not of message exchange. GET, PUT, POST,
> > DELETE... are operations performed on resource with varying degrees of
> > success.
> 
> The access and manipulation operations *are* messages.  I don't
> understand the distinction you're making.

I guess I'm making a distinction between mean and ends. Messages are the
means to transfer representations of resource state.  But the ends is the
access and manipulation of resource state, not the exchange of messages.

<snip/>

> > Whatever you are using you have to understand the semantics of the thing
you
> > are using. I'm not so hung up on the 'application' prefix.
> 
> Hmm, I guess I am hung up on them, because application semantics are
> special; they're at the top of the stack.
>
> > > If the resource state view is not important to them, why are they
using
> > > HTTP?
> > 
> > Because there is a binding available that provide features whose
semantics
> > they understand and because our charter mandated that we provide such a
> > binding.
> 
> I guess this relates to the point above; binding SOAP to an application
> protocol exposes more semantics than those exposed by the features and
> MEPs we've associated with the binding.  Specifically, application
> semantics are also exposed.  To quote Roy;
> 
> "The difference between an application-level
> protocol and a transport-level protocol is that an application-level
> includes application semantics, by standard agreement, within
> the messages that the protocol transfers.  That is why HTTP is called
> a Transfer protocol.  It is impossible to conform to an
> application-level protocol without also conforming faithfully to
> its message semantics."
>  -- http://lists.w3.org/Archives/Public/www-tag/2002Apr/0303

Firstly I agree with Roy, but I would also generalise this as:

"The difference between an N layer protocol and a M layer protocol is that a
N layer protocol includes layer N semantics, by standard agreement, within
the messages that the protocol transfers.... It is impossible to conform to
an N layer protocol without conforming faithfully to its message semantics."

With which I also agree.

> MB
> -- 
> Mark Baker, CTO, Idokorro Mobile (formerly Planetfred)
> Ottawa, Ontario, CANADA.               distobj@acm.org
> http://www.markbaker.ca        http://www.idokorro.com

Stuart
Received on Thursday, 4 July 2002 04:08:06 GMT

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