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Re: Protocol independence and application protocols

From: Mike Champion <mc@xegesis.org>
Date: Tue, 15 Apr 2003 08:42:30 -0400
To: www-ws@w3.org
Message-id: <oprnn784fqezizxn@smtp.comcast.net>

On Tue, 15 Apr 2003 00:18:43 -0400, Mark Baker <distobj@acm.org> wrote:


>
> Ok, great.  So was there a reason why you didn't support my proposal to
> talk about the pros and cons of protocol independence[1] in the WSA
> doc?

Exhaustion?  A sense that there are other topics that WSA needs to examine 
besides this? :-)

Your proposal was:

"Though envelopes sent over application protocols differ in meaning
depending upon which application protocol and method is used, the WSA
prescribes that application protocols shall be treated as if they were
transport protocols.  This has the following advantages and
disadvantages; [...]""

I could live with: Although from the underlying protocol's perspective Web 
services messages might appear to have different meanings depending on 
which operation is used to move the message body from one network node to 
another, the WSA takes the point of view that a Web services message has 
the same meaning irrespective of the mechanism by which it is delivered. 
This approach, often referred to as "tunneling" one protocol over another, 
is controversial, and should be undertaken in a specific application only 
after considering the advantages and disadvantages:

Advantages: Messages can be more easily bridged from one underlying 
protocol to another in a heterogenous environment .... Development tools, 
Web services, and application components can be written to the XML Infoset 
and SOAP processing model and abstracting away support for the underlying 
protocol(s) ....

Disadvantages:  .... [you suggest some, Mark]


> it simply does not possess the properties necessary to succeed on the
> Internet.

Remind me of what those are .... statelessness, visiblity, uniform 
interfaces?

FWIW, I personally could easily live with the conclusion that stateful, 
limited-visibility, heterogenous interface services are most appropriate 
for enterprise-scale rather than Internet-scale deployment.  But since 
that's where Web services are actually being deployed today, that's not a 
problem if the advantages outweigh the disadvantages.

Also, new generations of infrastructure are continually evolving to 
mitigate the disadvantages.  For example, application servers evolved to 
manage the disconnect between the stateless HTTP servers and the stateful 
applications that people wanted to access over the Web; SOAP/XML-aware 
firewalls are coming online that exploit the visibility that XML allows 
whereas Fielding (AFAIK) assumes that message bodies are opaque to 
intermediaries, and WSDL (and potentially RDF-based description languages) 
make heterogenous interfaces dynamically "understandable" [to a limited 
extent, of course] by both client side and service-side components.
Received on Tuesday, 15 April 2003 08:48:20 GMT

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