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RE: Issue: Synch/Asynch Web services

From: Cutler, Roger (RogerCutler) <RogerCutler@chevrontexaco.com>
Date: Mon, 11 Aug 2003 09:41:31 -0500
Message-ID: <7FCB5A9F010AAE419A79A54B44F3718E01817F41@bocnte2k3.boc.chevrontexaco.net>
To: "Sai Surya Kiran Evani" <evani@informatik.uni-freiburg.de>
cc: www-ws-arch@w3.org
I think that the answer to your original question is, "No" -- I have not
seen any discussion of these concepts in this group.  However, speaking
personally this looks very interesting.  If you're willing to keep
talking about this, I have some questions:
What is a bounded length queue?  Is this a reasonable model for
practical systems on the Web?
Granting that Web services can be viewed in this context, what is the
potential gain?  Do these theories provide logical foundations of some
sort that we might be able to lean on somehow?  Or do they draw
distinctions or derive results that might constrain or guide Web
services architecture?
I'm reaching here because I really don't know much about the theoretical
background.  I have heard of pi-calculus, but in a context that seems to
me a bit different.  I seem to recall Microsoft people claiming that
their XLang language, which I believe is something like a lower level
BPEL, or perhaps a precursor to BPEL, used (I think) as a basis for the
logic underlying their EAI product, Biztalk Server -- I think that they
claimed that XLANG has some sort of completeness because it is a
representation of Pi calculus.  This may be a bit confused, but it at
least gives you a hint where my personal knowledge level sits.  However,
based on this scanty knowledge I would have sort of expected things like
Pi calculus to come up in the Choreography group.  So that's what
motivates me to ask how you see this stuff applying to the architecture
of the Web services (other than through choreography)?
-----Original Message-----
From: Sai Surya Kiran Evani [mailto:evani@informatik.uni-freiburg.de] 
Sent: Monday, August 11, 2003 3:22 AM
To: Cutler, Roger (RogerCutler)
Cc: www-ws-arch@w3.org
Subject: Re: Issue: Synch/Asynch Web services


What I meant was that each WSDL port could be thought of as a queue and
a service which communicates using these ports as a process.

The two important theories dealing with communicating processes -
Communicating Sequential processes(Hoare), Calculus of Communicating
Systems(Pi-Calculus etc - Robin Milner) assume that message passing is
immediate or based on bounded length queues.

On the other hand, communication among processes with unbounded FIFO
queues has been studied using an abstraction called "Network of
Communicating Finite State Machines" to my knowledge. 


Cutler, Roger (RogerCutler) wrote:

	I would personally appreciate it if you would explain this a
little more
	-----Original Message-----
	From: Sai Surya Kiran Evani
	Sent: Saturday, August 09, 2003 10:44 AM
	To: www-ws-arch@w3.org
	Subject: Re: Issue: Synch/Asynch Web services
	Just curious if there would be anything defined regarding the
	behaviour of a web service. I guess the analysis of the systems
	- the provider or the invoker would be different in the cases of

	unbounded queues and bounded queues..
	Geoff Arnold wrote:

			Bottom line: From my point of view async/sync is
a question of 
			blocking or not, and completely separated from
the underlying 
			protocol. It just has to provide sufficient ways
to handle the 
			message exchange in the way desired by the

		If it were the case that sync/async were merely a
question of blocking


		or non-blocking, WSA (and SOAP, and.....) would have
nothing to say on


		the subject, since our specifications are silent on the
question of 
		However there is an alternative viewpoint (that
sync/async is a 
		property of message exchange patterns), and this has
		whatsoever to do with implementation, blocking,
threading and so 

Received on Monday, 11 August 2003 10:42:34 UTC

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