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Re: Terminology - What is a process? Was: Internal processes and/or external choreographies (was RE: Ev ents and States ...

From: Steve Ross-Talbot <steve@enigmatec.net>
Date: Tue, 15 Apr 2003 20:59:32 +0100
Cc: "'Howard N Smith'" <howard.smith@ontology.org>, <public-ws-chor@w3.org>
To: "Jean-Jacques Dubray" <jjd@eigner.com>
Message-Id: <C682E580-6F7C-11D7-A09B-000393AD2AA6@enigmatec.net>

JJ and Howard,

Whilst we could send such a question to Prof Milner he is pretty 
pressed for time. Lucian is a better bet because he understand the Web 
Services architecture and certainly has Prof Milner's blessing. He is 
also busy but I am happy to
pass on the request if you wish me to do so.

My own observations suggest that pi and/or higher order pi is rich 
enough and appropriate to use as a basis for expressing choreographies.

Cheers

Steve T

On Tuesday, April 15, 2003, at 07:06  pm, Jean-Jacques Dubray wrote:

>
>
>
> Following your comment that "everything" is a process, shouldn't we
> expect that any 100% pi-c based solution will follow the same fate of
> other "uni-cratic" systems like Java, C, SQL, COBOL, ... i.e. severe
> limitations/complexities outside the realm of applications for which
> they were designed (e.g. EJBs versus Classes).
>
> From what I can see the web-service architecture has a rich set of
> constructs that can only be diluated if everything becomes a "process".
>
> The way I understand the role of ws-chor is to provide a metamodel with
> which one can model "choreographies" message exchange between web
> services. If there is a requirement for this metamodel to be as simple
> as possible, there is also a requirement that this metamodel must be
> rich enough such that expressing choreographies does not become 
> "heary".
> Of course we can always talk about tool(s) breaking that hearyness, but
> then the babel effect comes into place where each tool coming with its
> "features" will in essence create semantic island which will make
> comparing choreography specifications difficult at best.
>
> With respect to pi-c no matter how I stear at it I don't see an 
> explicit
> choreography specification. All I see is the specification of the
> behavior of agents which are capable of communicating which each other.
> If you take the example: _xy.0 | x(u)._uv.0 | _xz.0, it expresses the
> behavior of each agent and the composition "point" but by no means the
> "choreography" is "visible" there. Furthermore, pi-calculus seem to be
> limited to request/response message exchange patterns (I'd be curious 
> to
> know how one would model complex MEPs).
>
> Ultimately, a ws-choreography can and should be expressed in 
> abstraction
> of the agents that will implement this choreography and how they will
> implement it.
>
> Respectfully, I would be very interested to know the opinion of Prof.
> Milner about whether a choreography specification is already present in
> the theory or not, and its relevance with respect to the design and
> binding of collaborating agents. Milner took the perspective of
> autonomous agent that need to communicate with each other via very
> simple protocols, he has not necessarily addressed the problem of
> expressing choreographies for which agent will be designed (or
> configured). Of course the problem are intimately related but aren't we
> looking at the specification (ws-chor) and the implementation 
> (pi-calc)?
>
> Overall what is needed is an appropriate metamodel for web service
> choreographies. We should leave the implementation details to the
> vendors where some could decide that the best way to implement a given
> "side" of the choreography is to use a pi-c interpreter, hence 
> compiling
> the choreography into a process definition.
>
> Jean-Jacques Dubray____________________
> Chief Architect
> Eigner  Precision Lifecycle Management
> 200 Fifth Avenue
> Waltham, MA 02451
> 781-472-6317
> jjd@eigner.com
> www.eigner.com
>
>
>
>>> -----Original Message-----
>>> From: public-ws-chor-request@w3.org
> [mailto:public-ws-chor-request@w3.org]
>>> On Behalf Of Howard N Smith
>>> Sent: Monday, April 14, 2003 10:07 AM
>>> To: public-ws-chor@w3.org
>>> Subject: Terminology - What is a process? Was: Internal processes
> and/or
>>> external choreographies (was RE: Ev ents and States ...
>>>
>>>
>>> David,
>>>
>>> You made a couple of remark which I'd like to comment upon:
>>>
>>> You said:
>>>> 1. I don't think I would call it "process buyerSeller" as buyer and
>>> seller are roles and they can have more than one choreography between
> them.
>>> I also like the word Choreography >rather than process (as you
> describe),
>>> so perhaps a better name would be something like "Choreography
>>> orderManagement".
>>>
>>> and:
>>>> 2. Following on in the same theme, using "process seller" and
> "process
>>> buyer" is ambiguous as you will have more than one process at the
> buyer
>>> and
>>> seller. So how about "process >acceptOrder" and "process placeOrder"
> where
>>> each has a property that identifies the role which performs the
> process
>>> giving you: "process acceptOrder, role seller" and "proccess
> placeOrder,
>>> role buyer".
>>>
>>> For the "process calculus people" in the group, everything is a
> process,
>>> even the humble integer. (I think that was what Assaf just naturally
> did).
>>> In the pi-calculus,
>>> everything is a process - formally. This group, and the industry at
> large,
>>> may have started to use the word "choreography" but the term has no
> basis
>>> in any
>>> previously published theory, and hence, everyone is using it and
> defining
>>> it differently. Similarly, to process calculus people, the seller and
> the
>>> buyer are
>>> also processes. In BPM as used in CSC, processes participate in
> processes.
>>> The result is also a process.
>>>
>>> This "everything is a process" position that process calculus people
> take
>>> is in fact quite real. It is the same position taken by object people
> in
>>> object systems.
>>> CSC defines BPM as really a new technology, based on processes. It
> depends
>>> upon implementations, which we call process virtual machines. The
>>> commonplace
>>> language we used in our book, BPM: The Third Wave, to explain this to
> the
>>> world at large is to talk about "first class citizens" in computing.
> Every
>>> technology
>>> has a conceptual center, sometimes defined very formally and 
>>> sometimes
>>> less
>>> so. To see what I mean here are a few first class citizens:
>>>
>>> - COBOL, the report
>>> - C, the pointer, function
>>> - Java, the object
>>> - EDI, the business element
>>> - XML, the tag
>>> - RDBMS, SQL, tuple, key
>>> - EAI, application interface
>>> - workflow, resource, task, case
>>>
>>> etc etc ... realise this is rough, but you get the idea ...
>>>
>>> The reason we identify the process as a new "first class citizen" is
>>> because in BPM process is not a byproduct of another stack of
> technology,
>>> but the central entity around which all computation and communication
>>> occurs. This is what gives BPM its ability to manipulate process, as
> RDBMS
>>> does relational data. It is what gives BPM its expressiveness in
> defining
>>> sophisticated meta-process models that adhere to other process
> semantics,
>>> for example:
>>>
>>> - project plans, schedules
>>> - B2B PIPs
>>> - workflow patterns, task allocation
>>> - collaboration patterns (votes, polls, committments etc)
>>> - supply chain models
>>> - other process languages
>>>
>>> It is what gives BPM it's completeness. What we have been looking for
> at
>>> BPMI.org and CSC, is a new first class citizen that can express
>>> many of the others, so that we can manage them as processes. A
> question
>>> that comes to my mind is:
>>>
>>> - Is there anything in this abstract "choregraphy" space that is NOT 
>>> a
>>> process, that cannot be "described" using process calculus?
>>>
>>> Thoughts?
>>>
>>> Howard
>>>
>>>
>>> ---
>>>
>>> New Book - Business Process Management: The Third Wave
>>> www.bpm3.com
>>>
>>> Howard Smith/CSC/BPMI.org
>>> cell             +44 7711 594 494 (worldwide)
>>> home office +44 20 8660 1963
>
>
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Received on Tuesday, 15 April 2003 16:00:13 UTC

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