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RE: Snapshot of Web Services Glossary

From: Assaf Arkin <arkin@intalio.com>
Date: Fri, 21 Feb 2003 10:26:13 -0800
To: "David Booth" <dbooth@w3.org>, "Martin Chapman" <martin.chapman@oracle.com>, <www-ws-arch@w3.org>
Cc: "'Hugo Haas'" <hugo@w3.org>

> -----Original Message-----
> From: www-ws-arch-request@w3.org [mailto:www-ws-arch-request@w3.org]On
> Behalf Of David Booth
> Sent: Friday, February 21, 2003 10:09 AM
> To: Martin Chapman; www-ws-arch@w3.org
> Cc: 'Hugo Haas'
> Subject: RE: Snapshot of Web Services Glossary
> At 04:35 PM 2/20/2003 -0800, Martin Chapman wrote:
> >hmmm don't like the defn of synchronous:
> I struggled with this one, and I'm not sure my proposed wording is ideal,
> but what I was trying to do was more clearly differentiate between
> synchronous and asynchronous.   The old definition was very vague.
> Somehow we need to convey the idea that with "synchronous"
> interactions the
> parties are synchronized in some way.  (!)  This could mean "at the same
> time", but in the case of two communicating parties it generally
> means the
> sending party waits for the receiving party to do something before the
> sending party continues.  Thus, they are "synchronized".  I
> couldn't figure
> out any better way to precisely capture this.  Any ideas?

Define that operation involves sending/receiving at initiator site, and
receiving/sending at respondent site. Define "time" to be bound by T1
(lower) and T2 (upper). I assume we can all agree to that.

Given just sending and receiving primitives (e.g. TCP send()/receive()),
initiator and respondent can agree on T1/T2 after concluding operation. With
just these two communication primitives they can synchronize their clock
within some resolution (but don't look for atomic clock type of
synchronization here).

> I agree that store-and-forward would NOT be synchronous, but I don't see
> store-and-forward as the opposite of direct communication.  Communication
> can certainly be indirect (i.e., go through intermediaries) but still be
> synchronous.  So although synchronous communication is often direct, I
> don't see that as a distinguishing characteristic.

An interaction can be synchronous even if it uses some store-and-forward
mechanism, even if both request and response are stored and forwarded.

Test for synchronisity of interaction is something like that:

If initiator sent request at time T1 then it can conclude that respondent
did not start performing interaction before time T1
If initiator received request at time T2 then it can conclude that
respondent did not continue performing interaction after time T2
(and vice versa)

You can clearly see this is not true for asynchronous interaction.


> >and
> >the fact that the reply (if any) comes back on the same communication
> >channel as the request.
> Interesting thought.  Must that always be true?  I could
> certainly imagine
> an input-output operation in which the input uses one
> communication channel
> and the output uses another.  So again, I don't see this as a
> distinguishing characteristic of synchronous communication.
> Anyone else have other suggestions for this definition?
> --
> David Booth
> W3C Fellow / Hewlett-Packard
> Telephone: +1.617.253.1273
Received on Friday, 21 February 2003 13:27:43 UTC

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