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RE: Abstract Bindable Choreography

From: Cummins, Fred A <fred.cummins@eds.com>
Date: Tue, 8 Apr 2003 19:32:04 -0500
Message-ID: <27C20ED5A6D3D511ADF30002A5D6464802A047C6@USPLM214>
To: "'WS Choreography (E-mail) '" <public-ws-chor@w3.org>

There seems to be several different issues involved in the discussion
of notation.  Let me share my perspective:

1. The target notation for WS-Chor should be XML so that the choreography
specification can be exchanged as part of establishing a relationship
between parties to a web services exchange.

2. It may be useful to have a more visual notation for developing 
examples and exploring problems.  This should not be normative for
this group.

3. The OMG has an RFP outstanding for Business Process Definition 
Metamodel which is intended to define a metamodel for businesss processes
including choreography, but without notation.  The purpose is to define
the modeling concepts to be used by modeling tools, to provide for the
integration of these models with other UML models, to provide for the
storage of these models in a MOF repository, and to provide a medium
of exchange using XMI.  The expectation is that this metamodel will
support a varity of notations and provide a common representation for
their exchange.

4. UML provides some notation for expressing processes (activity diagrams)
and exchanges (sequence diagrams) that may be useful, but they are not
likely to express what is needed in choreography since I doubt that
choreography was considered in their design, and they are not generally
accepted as good notations for expressing business processes.


> -----Original Message-----
> From: Assaf Arkin [mailto:arkin@intalio.com]
> Sent: Monday, April 07, 2003 3:53 PM
> To: Jean-Jacques Dubray
> Cc: 'Burdett, David'; 'Ricky Ho '; 'WS Choreography (E-mail) 
> '; 'Martin
> Chapman'
> Subject: Re: Abstract Bindable Choreography
> There are three issues here.
> 1. Does the fact that we use one notation prevents you from using a 
> different notation? Using the notation in a non-normative fashion 
> ensures that if you prefer to use a different notation you 
> can. We don't 
> marry the language to the notation, only use the notation to 
> clarify the 
> examples. So the notation should be considered on that merit.
> 2. Is the notation a good one to select for what you want to 
> achieve? I 
> argue that BPMN would be easier to use and read than, for 
> exampe, UML. 
> While it looks similar enough to UML, it has more explicit 
> distinction 
> between event types (messages, time-outs, faults) and better 
> handling of 
> roles, message direction, etc. So it leverages existing 
> experience, but 
> provides a notation that is easier to grasp at first glance.
> 3. Is the model the right one to use?
> There is one way to model choreographies which both BPMN and 
> UML take. 
> See for example RN PIPs. And I have seen it used before with EDI and 
> other communication specifications (e.g. Internet protocols, 
> distributed 
> algorithms). This approach is quite common in the B2B world, 
> it depicts 
> the separate responsibilities of each partner in the choreography. It 
> also maps well to the underlying mobile process model, which 
> can depict 
> complex choreographies, allow for better composition and reuse, etc.
> I know you disagree with this assesment and prefer a different model 
> which shows one activity shared by both partners. 
> Understandable. But if 
> we decide that the mobile process model is the better one to 
> use, then 
> BPMN seems like the best notation we can utilize. Since we've so far 
> discussed using BPMN to model choreographies that fit into this 
> category, let's keep the discussion along these lines and not 
> turn this 
> into a permathread about which model to use.
> arkin
> Jean-Jacques Dubray wrote:
> >  
> >
> >>>In fact, I think the last point is very important. The notation is
> >>>      
> >>>
> >self
> >  
> >
> >>>explanatory so it's easy to understand definitions - 
> including those
> >>>depicting multi-party choreographies - by just looking at 
> the diagram.
> >>>Just look at the example that Stephen gave and see if you 
> can easily
> >>>understand what's going on without having to read the BPMN spec.
> >>>
> >>>      
> >>>
> >
> >Actually, I would content that this is not as true as one 
> would believe,
> >yes you can clearly see the message exchange in an otherwise 
> forest of
> >internal activities in each respective party.
> >
> >My main point of contention with WSCI remains and this is why I don't
> >like BPMN when applied to choreography as well: the 
> choreography itself
> >is not represented, it is merely the association of "n" choreography
> >specifications (one for each partner) that one has to use to 
> understand
> >(an navigate) the overall behavior of the choreography (this is well
> >shown by Steven's examples). This creates an unnecessary level of
> >complexity that would hinder the understanding of a large 
> choreography
> >(look at what is currently needed to support a few messages 
> between two
> >parties). Other notations exist which show one single "neutral"
> >choreography without the use of "internal" activity and 
> business logic.
> >
> >
> >JJ-
> >
> >  
> >
Received on Tuesday, 8 April 2003 20:32:11 UTC

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