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Re: REST, Conversations and Reliability

From: Paul Prescod <paul@prescod.net>
Date: Tue, 06 Aug 2002 22:01:14 -0700
Message-ID: <3D50A99A.213B309A@prescod.net>
To: David Orchard <dorchard@bea.com>, www-ws-arch@w3.org

David Orchard wrote:
> 
> I understand the point you are making, which is about the scalability of
> reliability solutions that span trust domains.

And just when we were having so much fun dealing with specific
proposals. ;)

> But I'll decline the challenge to show proof of something that I'm hoping
> we're going to create.  I understand that you think we've tried and failed,

I want to make the point that the Waldo paper that Mark cites later is
interesting in that it claims that every few years a new set of
developers tries to tackle these intractable problems. 

"Every ten years (approximately),
members of the language camp notice that the number of
distributed applications is relatively small. They look at
the programming interfaces and decide that the problem is
that the programming model is not close enough to whatever
programming model is currently in vogue (messages
in the 1970s [7], [8], procedure calls in the 1980s [9], [10],
[11], and objects in the 1990s [1], [2]). A furious bout of
language and protocol design takes place and a new distributed
computing paradigm is announced that is compliant
with the latest programming model. After several
years, the percentage of distributed applications is discovered
not to have increased significantly, and the cycle
begins anew."

You may not feel that you are in the "language camp" but when you talk
about separating networking and reliability logic from application logic
it sounds to me like you are. In network-based applications, networking
and reliability issues are central to your application's logic.

I also feel that the paper offers compelling evidence that applications
*cannot be agnostic* about reliability issues. Reliability must be
worked into the fabric of the application logic:

"The limitations on the reliability and robustness of NFS have nothing
to do with the implementation of the parts of that system. There is no
"quality of service" that can be improved to eliminate the need for hard
mounting NFS volumes. The problem can be traced to the interface upon
which NFS is built, an interface that was designed for non-distributed
computing where partial failure was not possible. The reliability of 
NFS cannot be changed without achange to that interface [used by
programmer's to construct the application logic], a change that will
reflect the distributed nature of the application."

In other words, the programmer's interface and application logic must be
changed: reliability cannot be outsourced.

> but I think we have some new technology - like the web URIs, XML, SOAP,
> WSDL - as well as past experience that will help us.  And I think we can use
> these technologies in ways that loosely couple reliability to application
> semantics.

Every past attempt to solve this problem has built on technologies that
were isomorphic to URIs, XML, SOAP and WSDL. But there is no need
arguing specifics. You believe things are much different this time
around. I do not.
-- 
XML, Web Services Architecture, REST Architectural Style
Consulting, training, programming: http://www.constantrevolution.com
Come discuss XML and REST web services at the Extreme Markup Conference
Received on Wednesday, 7 August 2002 01:03:43 GMT

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