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RE: Myth of Loose coupling

From: Olivier Fehr <Olivier.Fehr@ofehr.com>
Date: Mon, 29 Sep 2003 13:29:21 +0200
Message-ID: <F92F63FC00C0AD4D88BECB3BCF90734B19E5@coyote.ofehr.com>
To: "Geoff Arnold" <Geoff.Arnold@Sun.COM>, "David Orchard" <dorchard@bea.com>
Cc: <www-ws-arch@w3.org>

In principle I agree that there is always coupling. But it certainly is
possible to talk about degrees of coupling.
If it makes sense to talk about degrees of coupling, what degrees of
coupling do we/should we have or define and what can we infer from these
degrees, e.g. loosely-coupled means MUST HAVE, MUST NOT HAVE, etc

So, I think David has a good approach on this.

-----Original Message-----
From: www-ws-arch-request@w3.org [mailto:www-ws-arch-request@w3.org] On
Behalf Of Geoff Arnold
Sent: lundi, 29. septembre 2003 06:33
To: David Orchard
Cc: www-ws-arch@w3.org


Nicely put.

On Friday, September 26, 2003, at 06:01 PM, David Orchard wrote:

> I'm posting a link as I was asked to before on the start of a 
> discussion on
> loose coupling.
> http://lists.w3.org/Archives/Public/www-ws-arch/2003Jan/0115.html
> I will say that I have come to have a somewhat revised view on loose
> coupling.  I would say that loose coupling is a combination of 
> properties:
> - extensibility, so that additional information can be added without
> breaking receivers
> - evolvable changes in the interface, so compatible changes can be 
> made.
> - rapidity of changes in the interface
> - on the web, the generic interface constraint, means that
> (browsers/search engines) are not dependent upon each site's protocol.
> - asynchrony, so that senders and receivers are decoupled in time
> - stateless messaging, so that senders need fewer messages and hence 
> less
> chance of communication errors
> - use of URIs for identifying resources.  This means that identifiers 
> are
> very constrained and easily transferred.
> - No vendor specific or platform specific constraints on any of the
> technologies used.
> I think one can then say that loose coupling is a property that is a
> combination of other properties as I've listed above.  And it seems 
> that
> changing each property/constraint increases the coupling.  For 
> example, a
> web service with no extensibility, that evolves rapidly in
> ways, an application specific interface, synchronous, stateful 
> messages is
> tightly coupled with it's clients.
> This would show that the Web is "mostly" loosely coupled because of
> extensibility/evolvability in http/html, slow changes in html 
> vocabularies,
> stateless messaging, vendor/platform agnostic.  Yet it is tightly 
> coupled in
> being synchronous.
> Another way of looking at this is that Web service technologies do not

> per
> se mean a service is loosely coupled, it is only through the 
> application of
> constraints to be loosely coupled.
> Seem reasonable?
> I think this notion of a "combination" property is similar to the 
> visibility
> property, which I argue is a combination of simplicity and percieved
> performance properties.
> Cheers,
> Dave
Received on Monday, 29 September 2003 07:29:34 UTC

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