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RE: [Requirements] Non-requirement for MEPs

From: Patil, Sanjaykumar <sanjay.patil@iona.com>
Date: Mon, 17 Mar 2003 11:05:02 -0800
To: "Fletcher, Tony" <Tony.Fletcher@choreology.com>, <ChBussler@aol.com>, <steve@enigmatec.net>, <public-ws-chor@w3.org>
Agree, except that perhaps we should keep the two issues (supporting MEP and supporting signals) separate.
Regarding MEP, I guess WSDL may not define all the MEPs for us, specifically the ones that have additional semantics in the context WS-choreography and which in the context of a single WSDL may map to one of the pre-defined MEP. For example, a multi-cast MEP in the context of a choreography that sends a request for quote to multiple parties may be perceived as a simple notification MEP by the individual services of the recipient parties. 
Basically, I think, we can expect WSDL to define only a set of basic MEPs, that are meaningful in the context of individual services. We, the WS-chor group may define the additional complex MEPs and perhaps we (along with the WSDL working group) should ensure that the the WS-chor defined MEPs can be decomposed into the WSDL defined basic MEPs.
The issue of signals on the other hand is orthogonal to the WSDL defined MEP. I guess, the signals will be defined by the WS-chor (and perhaps some other specifications) and their transmittal can be mapped to a pre-defined MEP. For example, the receival of a business message and sending an acknowledgement signal can be mapped to a request-response MEP. 
On a side note, I would however like to raise an issue related to the proper  scoping of the signals, whenever we define them. In some of the previous business process related work (such as RosettaNet), signals were used to represent simultaneously different meanings such as a notification of the status of the delivery of message and also the notification of the outcome of the business level content validation, etc. Although it was not a blocker issue, this overloading of the semantics of signals had kind of intermixed the different functional layers, making it harder to provide for exceptional handling, etc. 
We should perhaps identify clearly the signals that map to the WS infrastructure stack such as the message delivery guarantee and the ones that have application semantics such as business content-validation. With this, we would also be able to reuse support for the infrastructural signals from other specifications such as WS-reliability (whatever and wherever this spec is today!), etc and focus only on the business process level signals. 
Sanjay Patil 
Distinguished Engineer 
IONA Technologies 
2350 Mission College Blvd. Suite 650 
Santa Clara, CA 95054 
Tel: (408) 350 9619 
Fax: (408) 350 9501 
Making Software Work Together TM 

-----Original Message-----
From: Fletcher, Tony [mailto:Tony.Fletcher@choreology.com]
Sent: Monday, March 17, 2003 8:22 AM
To: ChBussler@aol.com; steve@enigmatec.net; public-ws-chor@w3.org
Subject: RE: [Requirements] Non-requirement for MEPs

Dear Colleagues,
I should make it clear that I was not thinking in terms of WSDL at all.  (I guess that by its nature this group will have to map onto WSDL as a 'lower' thing and so hopefully we can make use of WSDL's basic MEPs - we may just need a simple 'send' and 'receive' at the WSDL level (i.e. only 2 of its current 4 / 7 patterns) and we compose those at will to make other patterns at the WS-Chor spec level).
I was thinking in terms of the message pattern that is built into BPSS.  This called a Business Transaction and is a Request ( only mandatory part) from 'Requester' to 'Responder' followed by an (optional) receiptAcknowledgement from 'Responder' to 'Requester'  followed by an (optional) acceptenceAcknowledgement from 'Responder' to 'Requester' followed by an (optional) Response from 'Responder' to 'Requester'  followed by an (optional) receiptAcknowledgement from 'Requester' to 'Responder' .  The Request and Response are messages compiled by the driving application (/process).  The Acknowledgements are pre-defined messages structures were only the values are supplied on the fly.
So in BPSS a Business Transaction (that which I was meaning as a MEP) is the lowest layer of message sequencing.  Business transactions can be composed into sets known as binary collaborations (which will have a particular purpose) and can be built into higher level binary collaborations (with a wider purpose) and so on.  The highest layer of BPSS adds in multiple roles and the sequencing of the binary collaborations into a complete multi role collaboration.
The folks who designed BPSS believe that the Business Transaction message exchange pattern is all that is required to provide any *business* message exchange and are thus prepared to live with its restriction.  They may be correct, but personally I am not sure and feel that it may be safer to allow the users of the WS-Chor language to have freedom to design their own business message exchange patterns.
I do think that specifying some standard 'messages' (the things that BPSS calls signals) that users of the language can readily call up and invoke would be useful and should be added to the requirements
Best Regards     Tony
A M Fletcher
Cohesions 1.0 (TM)
Business transaction management software for application coordination
Choreology Ltd., 13 Austin Friars, London EC2N 2JX     UK
Tel: +44 (0) 20 76701787   Fax: +44 (0) 20 7670 1785  Mobile: +44 (0) 7801 948219
tony.fletcher@choreology.com     (Home: amfletcher@iee.org)

-----Original Message-----
From: public-ws-chor-request@w3.org [mailto:public-ws-chor-request@w3.org] On Behalf Of ChBussler@aol.com
Sent: 17 March 2003 15:38
To: steve@enigmatec.net; Fletcher, Tony; public-ws-chor@w3.org
Cc: ChBussler@aol.com
Subject: Re: [Requirements] Non-requirement for MEPs


I think it is preferrable not to be restricted to WSDL, but also allow for the inclusion of other definitions/mechanisms.


In a message dated 3/17/03 7:04:24 AM Pacific Standard Time, 
steve@enigmatec.net writes:

Subj:RE: [Requirements] Non-requirement for MEPs 
Date:3/17/03 7:04:24 AM Pacific Standard Time
From: steve@enigmatec.net
To: Tony.Fletcher@choreology.com, public-ws-chor@w3.org
Sent from the Internet 


I think that there is an implication of this exclusion. It is that the choreography would be tied to WSDL based MEP's. If however we make MEP's part of the scope then we could extend the reach of the groups
work to include non-WSDL based formalisms.


Steve T

-----Original Message-----
From: public-ws-chor-request@w3.org [mailto:public-ws-chor-request@w3.org]On Behalf Of Fletcher, Tony
Sent: 17 March 2003 13:26
To: public-ws-chor@w3.org
Subject: [Requirements] Non-requirement for MEPs

Dear Colleagues,

Just to put in a message what I stated at the inaugural F2F.

Non- requirement for MEPs:
It presently seems to me that it is a 'non-requirement' to standards message exchange patterns (MEP) as part of the WS-Chor work.  MEPs act as a constraint on what you can do, so if one, or more, are defined we will have to be very sure that users of the technique can live within that set of constraints without having to 'jump through hoops' such as extending the standard MEPs or having to chain them together to get the pattern they actually need.

We certainly need to specify the 'construct'  for sending a single message so that should be added to the requirements list.

We may also wish to standardise as part of the specification (in a normative appendix perhaps) some standard business messages, such as a generic error reporting message and an acknowledgement message

Best Regards     Tony
A M Fletcher

Cohesions 1.0 (TM)

Business transaction management software for application coordination

Choreology Ltd., 13 Austin Friars, London EC2N 2JX     UK
Tel: +44 (0) 20 76701787   Fax: +44 (0) 20 7670 1785  Mobile: +44 (0) 7801 948219
tony.fletcher@choreology.com     (Home: amfletcher@iee.org)

Christoph Bussler
Received on Monday, 17 March 2003 14:08:22 UTC

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