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Date: Mon, 17 Jan 2011 13:13:18 +0100
From: Georg Bauhaus <rm.dash-bauhaus@futureapps.de>
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Date: 2011-01-17T13:13:18+01:00
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On 17.01.11 11:40, Simon Wright wrote:
> "Yannick Duchêne (Hibou57)" <yannick_duchene@yahoo.fr> writes:
> 
>>                                                 there is *never*
>> something like stateful with web process. [...] state
>> at the client side, not a per-cession state at the server side.
> 
> Using AJAX, there is certainly state within one page... but even
> excluding that, there clearly _is_ per-session state on the server; of
> course, the browser has to identify the session concerned before the
> server can know where to continue from.

Should there be session state in a server at all?  Alternatively,

   State := Server_Side.Evaluate (POST request);

   if Is_Possible_State (State, Web Server Information) then
      ...
   else
      Send_Error_Indication;
   end if;

A request will carry enough information to signal state assumptions.

The gist of it is that there is a finite number of possible states
(and state histories) in a web interaction.  If a request
indicates one of these states (or histories), the server may
continue the interaction.  If possible, it may assume the
corresponding state regardless of actual histories. (Since, in any case
a client may use multiple tabs running the "same" web interaction,
create forged requests, switch computers, exchange cookies,
switch ethernet connections, move VMs, or send request caused
by viral infections ...)

The set of possible states can change while some web interaction
is going on. Model data may have changed in the mean time, since
multiple clients concurrently update data,  effects are as intended
by some request history, etc.
But there always is a set of states, and, therefore, there always
is a predicate to be called for testing a request.

Correct?