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Re: Doing Web services right

protocol design request response reply
Mike Champion wrote:
> On Wed, 12 Mar 2003 14:09:18 +0000, Bill de hÓra 
> <bill.dehora@p...> wrote:
>> The thing is, to do anything interesting, are the users being burdened 
>> with reinventing protocols? As Geoff Arnold pointed out recently, API 
>> and protocol design require very different mindsets and approaches. 
>> Just shipping data around, really means just shipping data around 
>> /with/ service level agreements.
> To be honest, this is something I'm having a hard time coming to grips 
> with.  

Ok, but you just need to see the way the industry is hovering around 
a nunber of reliable messaging standards, recent discssion on the 
W3C ws lists, or at a lower level in Java-land, the SOAP --> Servlet 
--> JMS idiom, or even SOAP-->ASP-->BizTalk, to realize that 
shiipping stuff around is a minimal expectation. Assuming the apps 
can talk, the next thing people want is the data Fedexed.

> The RESTifarians make a strong point that every WSDL file defines 
> a new "protocol", and that ordinary users can't be expected to grasp the 
> subtleties of protocol design.  Getting back to my original point, that 
> seems like saying that the specific message format that a CGI (or 
> ASP/JSP/etc.) backend expects is a "protocol."  

I don't buy the ordinary user excuse too much. But I do know it 
takes time and effort to craft anything halfway decent in terms of a 
protocol or MEP above beyond request-response, which contradicts or 
offsets to a degree the application integration speeds WS are 
supposed to offer. Maybe the tradeoff is still a good one. But now 
we're way of the XML chart...

> True in the literal 
> sense of the word "protocol" in English, but I'm not sure it means 
> anything more than "the minimal expectation by the server of the 
> information content needed to do its job" (which is my understanding of 
> the position that folks including Walter Perry and Sean McGrath 
> advocate).  

Which is entirely sensible. But we're talking about sequences of 
messages that don't compose so well from request-response pairs. 
Reliable sequences can require 5 or more messages for the endpoints 
to come to agreement. Nobody talks about tranasction-neutral XML 
databases; maybe that's more obviously dubious.

Bill de hÓra


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