W3C home > Mailing lists > Public > public-ws-chor@w3.org > December 2003

Re: Why workflow is NOT just a Pi-process

From: Assaf Arkin <arkin@intalio.com>
Date: Wed, 03 Dec 2003 11:06:39 -0800
Message-ID: <3FCE343F.5090903@intalio.com>
To: Jean-Jacques Dubray <jeanjadu@Attachmate.com>
Cc: Steve Ross-Talbot <steve@enigmatec.net>, public-ws-chor@w3.org

Jean-Jacques Dubray wrote:

> If you wanted to model an ERP, I contend that the level of nesting 
> (i.e. all the composed processes from user to DB would be impractical 
> to manage). Except for Intalio which took a very pure approach to 
> implementing pi, everyone is using pi with one or two levels of 
> composition (nesting). Which I think is the wise approach.
>
Is that a technical argument regarding Intalio's architecture and 
product capabilities, or an attempt to portray Intalio in a negative light?

I'm happy to dispute that statement on a technical basis and even 
demonstrate its fallacy. But in the meanwhile, I do cordially request 
that if you have a personal agenda against Intalio please, for the sake 
of all other members, consider taking it off the public mailing list.

> Hence other efforts to carve these boundaries, such as BPELa or 
> ws-cdl, and the comment that choreographies are complementary. I go 
> even further in my last email, there is a duality between choreography 
> and orchestration, as proven by the fact that BPML 0.4 (an 
> orchestration specification) was repurposed with little change in a 
> choreography specification (WSCI).

I've said that two years ago and used an early version of BPML (0.4) to 
illustrate that point by example. At that time my argument was rejected. 
I am glad to learn that we finally see eye to eye on this. Perhaps, 
moving forward we could see eye to eye on more subjects. It will 
definitely help advance the level of this discussion.

> Steve, you might understand a bit my fustration, after 5 years, of 
> attempting to contribute to defining a business process models at 
> BPSS, BPML and WS-CHOR, I very sadly see that we are going pretty much 
> nowhere, completely ignoring the basics of what we are doing. I was at 
> a meeting in Paris last week, where one strong BPMI player was 
> responding to my comment that I could not understand why after 4 years 
> of efforts we still did not have a business process standard that had 
> the concept of a "user" and "organization" like WfMC had in 1995. His 
> response was "errare humanum est" and that was being fixed. How is it 
> possible that someone designing a "Business Process" specification 
> forgets about the "user" like BPML and now BPEL? Well it is possible, 
> once you take an approach like Howard is taking. Sadly, it is only a 
> few individuals that decide what approach to take, in one of the most 
> undemocratic way.
>
Since we don't experience any difficulties representing users or 
allowing the human element to be introduced, and actually take pride in 
our human interface capabilities, I would say that we present solid 
evidence that this statement is not entirely accurate.

> So I reiterate my request: why are we spending all this time to create 
> specifications that are vastly incomplete and overlapping. Why can't 
> we all come to a point of discussion where we finally tackle this 
> problem, creating a solid infrastructure foundation (BPEL,ws-cdl,...) 
> on which the "business" semantics (i.e. the sugar) (BPML, ebBP...) can 
> be built? I think answering this question would prove very fruitful.
>
This change in strategy is more then welcome, I personally believe and 
have expressed my clear interest in unification of these specifications. 
But we have to acknowlege that considerable time was spent due to the 
need, which I fail to understand, to reject various ideas and 
specifications. Once we root out the NIH thinking, I believe we will 
find it much easier to get our work done in a collaborative fashion.

arkin


> Ciao,
>
> Jean-Jacques
> tel: 425-649-6584
> Cell: 508-333-7634
>
> -----Original Message-----
> From: Steve Ross-Talbot [mailto:steve@enigmatec.net]
> Sent: Wednesday, December 03, 2003 1:33 AM
> To: Jean-Jacques Dubray
> Cc: Greg Meredith; public-ws-chor@w3.org; 'Haugen Robert'
> Subject: Re: Why workflow is NOT just a Pi-process
>
>
> I really don't think that this debate is going anywhere.
>
> I could say that everything can be represented as assembler but does 
> that help me in any way?
> I could say that everything can be modeled in logic but does that help?
>
> Alas saying that workflow is just a pi-process is not helpful.
>
> The pi-calculus (and higher order forms of process algebra) can be 
> used to model many things, including workflow. After all the 
> pi-calculus is turing complete and has (as Greg Meredith has oft
>
> stated) a number of interesting properties that allow us to reason 
> effectively about pi-calculus models.
>
> I understand Howard's attraction to a simple unifying model of 
> computation, of which the pi-calculus is a candidate. So Howard is 
> correct in asserting that workflow is a pi-process but it's just not a 
> useful thing to say for most people.
>
> On the other hand JJ suggests that you cannot represent workflow as a 
> pi-process because it lacks the higher level semantics (roles etc). 
> Just because it doesn't support them as syntactic sugar doesn't mean 
> that you cannot do so.
>
> The fact that the pi-calculus unifies the notion of data and process 
> is not a bad thing. It is a good thing. It has a use in that you can 
> model interaction with data and with classical notions of process 
> using the same underlying model. This in turn allows you to reason 
> about the systems that you model more fully.
>
> JJ also suggests that the pi-calculus works well for low levels of 
> nesting. I'm not quite sure I understand what is meant by "levels of 
> nesting". But if this is to include or be equivalent to recursive 
> composition then the pi-calculus is scale invariant with respect to 
> composition. It doesn't change and so is well suited to as many levels 
> as you want to go to. So, unless I misunderstand, the assertion is 
> incorrect.
>
> On the other hand JJ's point does beg the question "is it useful to 
> model workflow using the pi-calculus?.
> To answer this (and I don't intend to at this point) we have to ask 
> another question, namely "what is it we want to know about a workflow 
> that we can only understand by leveraging the pi-calculus?".
>
> If the answer is nothing then it is not useful to say "workflow is 
> just a pi-process". If there is something then clearly it is useful to 
> say "workflow is just a pi-process".
>
> If it turns out that it is useful then we will be able to understand 
> in what context a workflow should be modeled in this way (is it just 
> the execution platform or the language that described the workflow?).
>
> Perhaps better minds that mine could provide a single paragraph on why 
> the pi-calculus is useful in this regard.
>
> Cheers
>
> Steve T
>
>
>
> On 3 Dec 2003, at 02:16, Jean-Jacques Dubray wrote:
>
> > We may also want to keep Phil Wainewright in the loop, he is keeping
> > track of the debate and already wrote a very good summary:
> >
> > http://www.looselycoupled.com/blog/2003_11_23_lc.htm#10701540100113058
> > 8
> >
> > This article could also be titled: "why pi does not matter..."
> >
> >
> > 2. I think what we meant to imply by using the title "Workflow is just
> > a Pi process" is that there is something foundational about the Pi
> > concepts that allow us to model higher level processes, including
> > workflow-like processes.
> > We could have equally written papers with the following
> > titles:
> >
> > ERP is just a Pi process
> > SCM is just a Pi process
> > B2B is just a Pi process
> > Adding Up is just a Pi process
> > Managing A List is just a Pi process
> > EAI is just a Pi process
> > Data is just a Pi process
> > etc
> >
> > <JJ>I think we should define what "models" means. If it means express
> > all the semantics of the things listed above as a pi-process,
> > Intalio's N3 designer tool might be falling a bit short.
> >
> > For instance, I understand that a PO business object can be modeled as
> > a process, actually it will require that all instance variable of this
> > object be a pi-process itself, not to mention the database in which it
> > is stored, and so on...
> >
> > I am wondering why SAP and PeopleSoft have not yet released a
> > pi-version of their ERP system?
> >
> > </JJ>
> >
> > Just to clarify. If you look at some of the swimlane diagrams in the
> > paper, each swimlane is a BPML process in its own right (the XML form
> > and notational form being just alternate notations).
> > <JJ>I think you just touched the fundamental issue I have with pi,
> > BPML/BPEL and Intalio's product
> >
> > As I understand it, Pi and Intalio's product do not allow for role
> > separation (since a role IS A process). Since everything is a process,
> > there is no way to introduce the notion of domain of control or
> > independent role, everything is capable of exchanging messaging with
> > everything at all levels (that looks pretty evil to me, though Howard
> > seems to argue that this is great in the paragraphs below),
> >
> > I can easily conceive that choreography is not not needed as long as
> > you have process composition, but what choreography buys you is
> > precisely this notion of domain of control that does not seem to exist
> > in what I have seen so far. Pi works wonders in a wireless system
> > where the levels of nesting of pi-processes are relatively low.
> > However, I cannot imagine the disaster for an ERP system or a workflow
> > where the level of nesting could reach infinity (in computers terms).
> >
> > This is precisely because this notion of domain of control does not
> > exist that BPEL/BPML are going through excruciating pain to create the
> > concept of an abstract process, to precisely define the boundaries
> > that do no exist in the theory. As a matter of fact, pi just by
> > itself, cannot cross company boundaries. I think that this is what
> > howards says in the next two paragraphs.
> >
> > Maybe there is a business opportunity to run Intalio's Process Virtual
> > Machine in an ASP model, running all pi-processes in the world. Then
> > the problem will be solved.
> >
> > </JJ>
> >
> >
> > The process virtual machine within the BPMS creates end to end
> > processes out of piecemeal processes at all levels. This is where the
> > Pi concepts come in, since the interaction between swimlanes is of
> > course mobile behavior as defined by Milner. We chose email as an
> > example as it is a recusive process with this characteristic. We have
> > found similar characteristics with change management processes, record
> > keeping processes etc. We see no correspondence between these and
> > typical workflow processes as WFMS have been typically applied in
> > business.
> > It feels very different to me in practice.
> >
> > I believe that the significance of choreography lies at the heart of
> > this, which is kind of why a subset of BPMI.org members submitted
> > WSCI, based on BPML, to this group, as a first step towards
> > unification. After all, it is WSCI-territory that allows multiple
> > technologies from existing players (even if they have no intention to
> > build a BPMS) to be used in conjunction with each other.
> >
> > Howard
>
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-- 
"Those who can, do; those who can't, make screenshots"

----------------------------------------------------------------------
Assaf Arkin                                          arkin@intalio.com
Intalio Inc.                                           www.intalio.com
The Business Process Management Company                 (650) 577 4700


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Received on Wednesday, 3 December 2003 14:29:03 UTC

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