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Re: Stateful Web Services...

From: David Booth <dbooth@w3.org>
Date: Wed, 03 Nov 2004 18:14:09 -0500
To: Mark Baker <distobj@acm.org>
Cc: David Orchard <dorchard@bea.com>, www-ws@w3.org
Message-Id: <1099523649.3419.181.camel@nc6000.w3.org>

Mark,

On Wed, 2004-11-03 at 14:15, Mark Baker wrote:
. . .
> Hold the phones!  Except for credit card info, which many people would
> probably before not be stored on the server anyhow, I can't imagine a
> scenario in which any of those things would need to be sent in each
> request.  I would guess that you're confusing the different kinds of
> state.  

I think the problem is one of language, since I know David Orchard
understands the difference you're describing.  We do not have clear
enough language/terminology for identifying these two concepts and
distinguishing between them.  I think this has been a major impediment
to discussions around them, and to people's understanding of them.

> Stateless interaction is a constraint on connectors, not
> components.  

I personally think the term "stateless interaction" is misleading, and I
think that Roy Fielding's use of the term "stateless" or "statelessness"
in his thesis is unfortunate, because people who are not aware of his
particular use of the term consistently misunderstand it.  In section
3.4.3 of his thesis he explains what he means:
http://www.ics.uci.edu/~fielding/pubs/dissertation/net_arch_styles.htm#sec_3_4_3
[[
Each request from client to server must contain all of the information
necessary to understand the request, and cannot take advantage of any
stored context on the server.
]]

I personally think the term "context-free" might have been a better
choice.  

> Said another way, it's fine to have a service remember
> stuff (component state), like a wishlist or order history, but what's
> not fine is if a message's semantics are a function of that state, 

That's a much clearer explanation.  I think the confusion comes up when
referring to the concept with a brief noun phrase like "stateless
interaction".  

I'm toying with the phrase "context-free message semantics" to refer to
this concept.  What do you (and others) think of this term?  

(I am aware of the use of the term "context-free" in "context-free
grammers", but I don't see that as a problem.)


-- 

David Booth
W3C Fellow / Hewlett-Packard
Received on Wednesday, 3 November 2004 23:14:10 GMT

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