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Debating on the usefulness of supporting a) Stateful Web Service Instances b) Stateful Interaction

From: marco <marco.adragna@kellogg.ox.ac.uk>
Date: Thu, 19 Jun 2003 15:15:22 +0200
To: <www-ws@w3.org>
Cc: <Savas.Parastatidis@newcastle.ac.uk>, <umit.yalcinalp@oracle.com>, "'Jim Webber'" <jim.webber@arjuna.com>, "'Steve Graham'" <sggraham@us.ibm.com>, "'Krishna Sankar'" <ksankar@cisco.com>
Message-ID: <000201c33664$d91b7270$5b00000a@marcoadragna>

I have been asked to move the discussion on stateful service instances
and stateful interactions to this list.
I think that Steve Graham as the Global Grid Forum invited expert 
would be the best person to summarise OGSI ideas on a) and b) 

Web Service composition languages have already some notion of a) and b)
Here we are talking of a) and b) in relation to a single non-composed
web service.

Today standard web services don't support:
a) The concept of stateful service instance
b) Stateful interaction 
-  Object passing, neither by value nor by reference

As a working definition of state of a software system  we could say that
"Is a condition that captures history of the system and influence how
the system behave in specific circumstances."[A.M. Davis - 1993 -
Software requirements]
A generic server supporting stateless interaction, process each message
on its own. 
If stateful interaction is supported, each message is interpreted in
relation to a state, in a context. 
A stateful software system can have stateless interactions. 
Today, a Web Service might be considered a stateful software system,
that support only stateless interactions. 
On the other hand, a) and b) are achieved in custom ways. (e.g. OGSI)

Would it be appropriate for web service standards to support a) and b) ?
Is it appropriate for the web service community to implement a) and b)
or is that a wrong OO mindset that we should abandon ?

Let me again remember that we are not talking about composition
that already have concepts that bear some resemblance with a) and b) 
(e.g. "business process instance" and "message correlation")

In this debate, I see the following main positions, please do suggest

-ab:  a) and b) must never be performed, not even in custom ways. 

-a :  b) can be performed in custom ways, but not a)

 0 :  a) and b) can be performed, but only in custom ways

+b :  Web service standards should support b), but not a)

+ab:  Web service standards should support both a) and b)

My position is currently close to +b, please cast your vote ;)

I have not included a) but not b) positions, because I think that if
full a) support is provided, 
then a form of b) must exist. But one could debate on this too ;)

Marco Adragna
Kellogg College
Oxford University
(Chief of R&D for Hit-Com.It)
Received on Thursday, 19 June 2003 09:18:40 UTC

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