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RE: On the Operation Name Mapping requirement

From: Glen Daniels <gdaniels@sonicsoftware.com>
Date: Mon, 4 Oct 2004 11:30:22 -0400
Message-ID: <80A43FC052CE3949A327527DCD5D6B2785BEA8@MAIL01.bedford.progress.com>
To: "Savas Parastatidis" <Savas.Parastatidis@newcastle.ac.uk>, <www-ws-desc@w3.org>


Hi Savas, all:

The idea of the ONM requirement is that the description should, in some
way, give you a hint as to how a particular operation is determined in
the absence of unique wire signatures.  In the case below, there is no
conflict, since one operation is in-out and the other is out-in.
Therefore, from the service's point of view, it is either going to
receive a GameOver message (and therefore the operation is
reactor:GameOver) or itself decide to send one (and therefore the
operation is intiator:GameOver).  The wire signatures are enough to
determine which is going on.  If both send them at the same time, I
would imagine that both operations would be invoked simultaneously,
generating a pair of equivalent messages in response.

To extrapolate out a little from what you say below, if you're
interested in modeling a system which has a complex state machine
involving lots of decision points based on arbitrary ordering of
incoming messages, I don't think WSDL is really what you want.  I would
think you'd use something like BPEL or BPML for this.  WSDL is
essentially about Web Service *operations* and that's why we have the
ONM requirement - if you can't distinguish which operation you're
talking about, you may as well just have an undifferentiated bag of
messages and not use WSDL at all.

--Glen 

> -----Original Message-----
> From: www-ws-desc-request@w3.org 
> [mailto:www-ws-desc-request@w3.org] On Behalf Of Savas Parastatidis
> Sent: Monday, October 04, 2004 4:51 AM
> To: www-ws-desc@w3.org
> Subject: On the Operation Name Mapping requirement
> 
> 
> Dear all,
> 
> Jim Webber and I are trying to get our heads around the 
> Operation Name Mapping (ONM) that exists in the current draft 
> at the interface level but will be moving to the service 
> level, as I read in one of the threads, in the next draft. 
> 
> We have been working on a very simple Noughts-and-Crosses 
> (tic-tac-toc) example for using SOAP and WSDL. The two 
> players are effectively two services exchanging messages. The 
> description of each of the services has to be symmetric, if 
> we are to reason about their ability to meaningfully exchange 
> messages. This means that we have to describe both the 
> "initiating" and the "reacting" message exchanges. Here's 
> what I mean...
> 
> <definitions targetNamespace="nac:interfaces:initiator">
>   <interface name="Player">
>     <operation name="GameOver"
> pattern="http://www.w3.org/2004/08/wsdl/out-in">
>       <output element="nac:game-over" />
>       <input element="nac:game-over" />
>     </operation>
>   </interface>
> </definitions>
> 
> <definitions targetNamespace="nac:interfaces:reactor">
> <interface name="Player">
>   <operation name="GameOver"
> pattern="http://www.w3.org/2004/08/wsdl/in-out">
>     <input element="nac:game-over" />
>     <output element="nac:game-over" />
>   </operation>
> </interface>
> 
> A Web Service that supports both these roles is described as:
> 
> <interface name="Player" extends="initiator:Player reactor:Player" />
> 
> What do the above interfaces mean? The first one tells us 
> that the service at some point will send a <game-over> 
> message and will expect to receive a corresponding 
> <game-over> message as a result. The second interface tells 
> us that if a service receives a <game-over> message, it will 
> respond with the same message. It's just happens that the 
> logic of the services requires that the messages are the same. 
> 
> Since we are in a loosely coupled world, we don't really know 
> which of the two players will send the <game-over> message 
> first, so we need to support both behaviours at each service. 
> This is absolutely fine since the logic of the two services 
> can cope with the scenario. "Oh... I just received a 
> 'game-over' message. The other player is telling me 
> something. I have to reply accordingly". Or, "Oh... I just 
> received a 'game-over' message as a reply to the one I 
> previously sent. That's the other player's response". And 
> "what if both endpoints send the same message, at the same 
> time?" you ask. Well, we use WS-Addressing to cope with this 
> situation ("ReplyTo" header).
> 
> 
> However, the ONM requirement doesn't allow our services to be 
> described in this way since the wire format is the same for 
> both GameOver operations. The service logic requires us to 
> send messages <game-over> messages on the wire (and this 
> works in our implementation) but WSDL 2.0 doesn't allow us to 
> describe it. Should WSDL be so restrictive and direct us 
> towards a particular way of describing our services?
> 
> We can think of other business cases where it is the service 
> logic that determines the dispatching of a particular 
> operation (based on contents, protocol, etc.) and not the 
> uniqueness of the wire format.
> 
> We'd be interested in the WG's comments.
> 
> Regards,
> Savas & Jim
> 
> 
> 
> 
> 
Received on Monday, 4 October 2004 15:30:15 GMT

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