Re: [wsbpel] Abstract BPEL (was RE: [wsbpel] FAQ)

["Ben Bloch" <ben_b54@hotmail.com>]

Tony,

I absolutely concur that the spec can and probably should do a better job of
describing what abstract processes are, including their relationship to and
potential unboundedness from executable processes. In fact, if this could
somehow be raised as an issue, perhaps the editors (of which I am one) can
take a swag at this. It would make the spec more readable and show the
value(s) of abstract processes themselves.

I also agree that individual abstract processes should not be dependent upon
one another to be able to operate.  However, one process IMO should be able
to learn or at least be influenced by the state (eg failure) of another
process, perhaps from the process in question itself, a coordination or
monitoring service (more likely) or some other mechanism.

And lastly,  if I could focus in on the last sentence about your demo:
"In a nutshell, it shows how we can verify that web service systems
(described by BPEL abstract processes) will communicate successfully, and
how we can detect and visualize errors."
Could you please define "successful" on this context? And, no, I won't be
going to the conference you speak of, but I'd love to somehow see it anyway.

Ben



how they compare to WSDL.
----- Original Message ----- 
From: "Tony Andrews" <tandrews@microsoft.com>
To: "Furniss, Peter" <Peter.Furniss@choreology.com>; <ygoland@bea.com>;
"John Evdemon" <jevdemon@microsoft.com>; <wsbpel@lists.oasis-open.org>
Sent: Thursday, October 23, 2003 2:30 PM
Subject: RE: [wsbpel] Abstract BPEL (was RE: [wsbpel] FAQ)


Thanks for jumping in on this Peter. That's a pretty good summary of my
position. Certainly, what's missing from BPEL today is a way of
describing how individual BPEL abstract processes can be combined
together in a precise way. That is a non-trivial problem in itself, and
while such a description would be of great interest to BPEL, I don't
think that the two should be dependent on one another. One might well
wish to describe the connection of web services whose behaviors are not
specified (or are not specified using BPEL).

Satish pointed to some of the rationale for describing the behavior of
the individual participants rather than taking a more neutral view of
the interaction. On a very practical level, a single-party view has
other benefits as well. It allows systems to be composed using either a
unilateral or bi/multi-lateral approach. Each abstract process
represents the behavior of one service, so it's in a form that can be
directly leveraged by developers to seed or verify their
implementations.

Historically, I believe this approach has also been widely used in
network protocol design. The TCP connection protocol, for example,
speaks of server states (CLOSED, LISTEN, SYN-RECEIVED, ESTABLISHED) and
client states (CLOSED, SYN-SENT, ESTABLISHED) and describes the behavior
of each party in terms of its own local observations and state
transitions. And as Satish was saying, in a neutral model the
(potentially many) race conditions that might arise would have to be
modeled explicitly while in an individual view they still exist but need
not be enumerated.

I'll also just echo a couple of important points that Peter raised.
First, the existence of an abstract BPEL process says *nothing* about
the way in which it is implemented. In fact, we'll probably start
describing existing services long before the first BPEL-compliant
execution engine runs its first process. In that respect, it's very much
like WSDL - purely descriptive.

Second, the interface/implementation relationship is a key point and
gives users a great deal of flexibility. Multiple implementations of a
single interface will be routine. But I think it will also be common for
services to implement multiple abstract process behaviors simultaneously
- perhaps as a "server" in one protocol and a "client" in another.


I don't think abstract processes are very well motivated in the spec
today. We should probably say more about their independence from
implementation and about their relationship to executable processes. We
should also say something about the formal methods that they are
intended to support - certainly, the limitations on abstract processes
were put in place with very specific analytic approaches in mind (i.e.
model-checking).

I have a demonstration of this that I'll be showing at the Microsoft
developer conference in Los Angeles next week. If anyone in the TC will
be attending, please stop by the Microsoft Research booth to say hello
and see the demo. In a nutshell, it shows how we can verify that web
service systems (described by BPEL abstract processes) will communicate
successfully, and how we can detect and visualize errors.

Tony

> -----Original Message-----
> From: Furniss, Peter [mailto:Peter.Furniss@choreology.com]
> Sent: Wednesday, October 22, 2003 4:42 PM
> To: ygoland@bea.com; John Evdemon; wsbpel@lists.oasis-open.org
> Subject: [wsbpel] Abstract BPEL (was RE: [wsbpel] FAQ)
>
> Some of Yaron's comments on the FAQ (most of which I agree
> with) seem to relate to the power of abstract BPEL
>
> paragraph from the proposed FAQ:
>
> <quote>
> The Business Process Execution Language is a XML-based
> language for formally describing interoperable business
> processes and business interaction protocols.  It defines how
> web services are connected together and in what sequence in
> order to accomplish a particular task
>
> </quote>
>
> to which Yaron comments :
>
> <quote>
> BPEL only provides a description of the behavior of a single
> player in a business process protocol. Since protocols
> require, by definition, more than one player BPEL is by
> definition unable to completely describe a business process
> protocol or to specify how different processes interact
> beyond describing the behavior of a single participant.
> Therefore I think this paragraph should be struck.
> </quote>
>
> which was very much my view until I had a conversation with
> Tony Andrews and got a better understanding of his
> presentation from the first face-to-face (
> http://www.oasis-open.org/archives/wsbpel/200305/msg00172.html
> ). It seemed some things I had thought would be necessary,
> and which I hadn't seen stated, and so assumed were not in
> view, were definitely
> intended/expected:
>
> - there can be multiple abstract definitions for a
> single executable, each specifying the dynamic behaviour of
> one (or set of
> related) interfaces, with the other interfaces handled by
> opaque assignment; the choice of how many of these there are,
> their level of opacity and the interfaces covered is a
> design/viewpoint question
>
> - there can be (and need to be for the "global"
> picture) abstract bpel definitions for processes that are
> never going to be in bpel - not least because some are "leaf"
> processes in the web-service world, and do real work on
> databases or visible effect on GUIs etc.
> rather than just defer to yet another web-service, which is
> all executable bpel can do
>
> - there can be multiple executable processes matching a
> single abstract definition - this is just an
> interface:implementation relationship
>
> (Apologies to Tony if I've mis-represented him). They
> obviously have some exciting implications for what bpel tools
> in general might do (especially the middle one - how on earth
> do you show compatibility between abstract bpel and a legacy
> app written in cobol with a web-service front end)
>
> But these don't seem to be in the spec. (last one might be).
> Should it be left to interpretation (and, no doubt, some books) ?
>
> There's also the possibility of stating the rules (guidelines ?
> constraints ?) involved in the two abstract bpel definitions
> that make up either side of a business protocol.
>
>
> (I should possibly mention that I was for a long time very
> sceptical about whether bpel or things like it was the way to
> do this, and thought it could be done with a simpler, less
> procedural approach. but gradually I found my vague "ideal"
> was getting necessarily more complex and needing more
> functionality - in fact heading towards somehting much like
> on abstract bpel)
>
> Peter (speaking for himself)
>
>
>
> > -----Original Message-----
> > From: Yaron Goland [mailto:ygoland@bea.com]
> > Sent: 22 October 2003 23:09
> > To: 'John Evdemon'; wsbpel@lists.oasis-open.org
> > Subject: RE: [wsbpel] FAQ
> >
> >
> > Some comments
> >
> > > -----Original Message-----
> > > From: John Evdemon [mailto:jevdemon@microsoft.com]
> > > Sent: Tuesday, October 21, 2003 12:44 PM
> > > To: wsbpel@lists.oasis-open.org
> > > Subject: [wsbpel] FAQ
> > >
> > >
> > >  <<WSBPEL DRAFT FAQ.txt>> Hello all,
> > >
> > >  A while ago I asked for feedback on a TC FAQ.  I have attached a
> > > draft that incorporates some initial feedback from Monica and Ugo.
> > > Please respond with any additional questions or concerns.
> > >
> > > If there is no feedback by 10/28 I will assume the TC is
> happy with
> > > the current version (attached) and submit it to OASIS.
> > >
> > > Thanks!
> > >
> > > John
> > >
> > >
> >
>
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>

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