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Re: New Paper available for PDF download: Workflow is just a Pi process (or WFM is not BPM)

From: Andrew Berry <andyb@whyanbeel.net>
Date: Tue, 18 Nov 2003 06:13:26 +1000
Cc: public-ws-chor@w3.org
To: Jean-Jacques Dubray <jeanjadu@Attachmate.com>
Message-Id: <80D48BFB-193A-11D8-B79E-0003936786BC@whyanbeel.net>

Jean-Jacques,

Briefly, yes, you can still do it without a broker.  My PhD thesis 
described (and I built) such a system.

Ciao,

AndyB

On Tuesday, November 18, 2003, at 02:17  AM, Jean-Jacques Dubray wrote:

> Andrew:
>
> I like your point and I am not trying to disagree with it. John Yunker 
> made a similar comment in ebBP, as a possible evolution to ebXML BPSS 
> which does not yet have this notion of partial state or "distributed 
> shared states". (it can be emulated, but the idea is to make them 
> first class citizens of the spec).
>
> I think your point also raises a fundamental question, which I thought 
> I knew the answer, but I now have some doubts.
>
> I thought up until now that a choreography (or even an orchestration) 
> of messages could be expressed, in abstraction of all other concepts 
> like partial state. In particular, I am convinced that as soon as you 
> bring partial state in, you also have to bring something like an 
> "object" or a business object into the mix (PO.paid), as most of the 
> states are often related to the state of such object (e.g. purchase 
> order paid). Then where does it ends, is the "B" layer the lowest 
> common denominator to SOA?
>
> So I believed that there is this pi-underground world (that has 
> nothing to do with the "B" or "W" words). At this level, we deal only 
> with message exchange (the "state" of the choreography can be derived, 
> not only from the messages that have been exchanged, but also from 
> their content, described in a very abstract and atomic way). One can 
> formally demonstrate that a choreography is a state machine in the 
> mathematical sense.
>
> Unfortunately, if other concepts are needed at the lowest level, then 
> pi might not work. I can see the wonders it does to model a variable 
> or a const as a process, but unfortunately this is of limited value to 
> solve the "C", "B" and "W" problems.
>
> What is your opinion on this? Reading your comment, I would conclude 
> that a pi-layer is not possible or are you saying that a message-layer 
> is possible but pi is not the right formalism for that.
>
> Thanks,
>
> Jean-Jacques
> tel: 425-649-6584
> Cell: 508-333-7634
>
> -----Original Message-----
> From: Andrew Berry [mailto:andyb@whyanbeel.net]
> Sent: Monday, November 17, 2003 2:59 AM
> To: Howard N Smith
> Cc: public-ws-chor@w3.org; W.M.P.v.d.Aalst@tm.tue.nl
> Subject: Re: New Paper available for PDF download: Workflow is just a 
> Pi process (or WFM is not BPM)
>
>
> Howard,
>
> You have a fundamental problem with the choice of Pi Calculus: there 
> is no concept of locality or partial state. In choreography and web 
> services in general, you can guarantee that participants (processes) 
> are physically distributed and need to make choices based on a partial 
> view of state.  To successfully model, program and reason about these 
> processes, you need to be able to identify and reason about partial 
> states.
>
> Consider your deferred choice semantics.  If the processes identified 
> as choices are physically distributed, you *cannot* make a choice 
> without synchronisation of processes because distinct choices can be 
> made in a truly concurrent fashion.  Pi Calculus has no way of 
> identifying this issue, let alone reasoning about it.  Explicit 
> synchronisation processes, while solving the problem for a given 
> process, require that the programmer reason about distribution and 
> locality outside the bounds of the Pi Calculus semantics.  I would 
> therefore argue that a worflow and in particular a choreography is not 
> a Pi Process.
>
> Ciao,
>
> AndyB
>
>
> On Wednesday, November 12, 2003, at 03:00  AM, Howard N Smith wrote:
>
> >
> > Choreography pioneers,
> >
> > Following a short conversation with Steve R-T, he agreed for me to
> > send you this paper.
> > It is intended as a draft for discussion.
> >
> > The paper is new information. It shows how, based on BPML, it is
> > possible to model all of the advanced workflow patterns identified by
> > workflow theorists, whereas most workflow engines only support approx
> > 50% of patterns directly and very few of the advanced patterns.
> > In addition, it gives insights into the BPML implementation inherent
> > to a BPMS, and how a BPMS is able to support many process models not
> > supported by workflow technology.
> > Screenshots from Intalio|n3 BPMS are given as examples. Further, the
> > workflow engine itself can be modelled in BPML, as reusable processes
> > for use in end-to-end processes. The paper was written to more fully
> > explain the work of BPMI.org and its direction in creating BPMS
> > foundation technologies.
> >
> > Peter Fingar and I have taken great care with this paper, and do hope
> > it adds to the understanding of BPML/BPMI/BPMS direction. While the
> > paper cannot present proof of these claims, you can consider it a
> > report on the work so far.
> >
> > The paper can be downloaded from:
> >
> > http://www.bpm3.com/picalculus/workflow-is-just-a-pi-process.pdf
> >
> > Regards,
> >
> > 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
> >
>
Received on Monday, 17 November 2003 15:11:09 GMT

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