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Re: Myth of Loose coupling

From: Geoff Arnold <Geoff.Arnold@Sun.COM>
Date: Sun, 28 Sep 2003 21:32:48 -0700
To: David Orchard <dorchard@bea.com>
Cc: www-ws-arch@w3.org
Message-id: <FB0728C3-F235-11D7-B492-000A95718676@sun.com>

+1

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 applications
> (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 incompatible
> 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 the
> 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 00:32:26 GMT

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