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RE: [Requirements] Non-requirement for MEPs

From: Assaf Arkin <arkin@intalio.com>
Date: Mon, 17 Mar 2003 17:38:12 -0800
To: "Patil, Sanjaykumar" <sanjay.patil@iona.com>, "Fletcher, Tony" <Tony.Fletcher@choreology.com>, <ChBussler@aol.com>, <steve@enigmatec.net>, <public-ws-chor@w3.org>
MessageI'm going to do the "hot potato" thing and suggest that we leave
those issues that are not specific to choreography to other working groups.

For example, signals. How do you represent the fact that a message must be
acknowledged? Let's say WS-Chor comes up with a solution. Can you use it
with a service that it no used in the context of any defined choreography?
Or do we have one way to do it in WS-Chor and another in WSD?

What about WS-RM (1 and 2) which already deal with that issue. Do we come up
with yet another solution for sending/receiving acks? Do we try to model
their approach with WS-Chor? Did anyone identify the need to use WS-Chor to
define these acks?

Try as I may I only found one sequence set that is parameterized by the QoS
requested. So we can exchange different sequences, but it appears to me that
just exchanging different QoS policies would be easier (to write, validate
and process). This seems more of a problem for WS-Policy to provide the
framework, and WSD to allow these patterns to occur within the operation (so
not to affect it's abstract definition).


  -----Original Message-----
  From: public-ws-chor-request@w3.org
[mailto:public-ws-chor-request@w3.org]On Behalf Of Patil, Sanjaykumar
  Sent: Monday, March 17, 2003 11:05 AM
  To: Fletcher, Tony; ChBussler@aol.com; steve@enigmatec.net;
  Subject: RE: [Requirements] Non-requirement for MEPs

  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
        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

          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 20:39:21 UTC

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