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RE: Internal processes and/or external choreographies (was RE: Ev ents and States ...

From: Cummins, Fred A <fred.cummins@eds.com>
Date: Thu, 10 Apr 2003 21:43:28 -0500
Message-ID: <27C20ED5A6D3D511ADF30002A5D6464802A71480@USPLM214>
To: "Burdett, David" <david.burdett@commerceone.com>, "Cummins, Fred A" <fred.cummins@eds.com>, Assaf Arkin <arkin@intalio.com>
Cc: "'jdart@tibco.com'" <jdart@tibco.com>, public-ws-chor@w3.org

David,

My view is that the scope should be external only, but for now
that should be the same as external first.  There may be many
implementations of a choreography with diverse processes as
appropriate to the particular processes.  Consequently, there
must be a clear separation between external and internal, and
the same choreography should be suitable for designing the
various internal implementations that marry to it.

I will be useful for tools to be able to validate the compatibility
of an internal process with a choreography (but not necessary).
In any event, the choreography should be specified such that this
compatibility can be determined, hopefully in a straightforward
manner.

Essentially, a participant must send a message when in an 
external state that calls for it to send a message, and the message
must be such that it will cause the recipient to transition to
the state desired by the sender based on the choreography.  A
participant has no control over the other participant(s) except
through sending an appropriate message--it cannot control what the
other participant sends, when it is sent, or if it is sent at all.

I suggest that the proper actions of a participant can be defined
by its public state machine.  Typically, each state will have two
or more exit transitions that depend on what is sent or received.
The selection of the exit transitions is made by the message sender
(unless there is an error or time-out which may be viewed as a
third message/transition type).

So an internal process can be validated against the participant's
public state machine specification.

Fred 

> -----Original Message-----
> From: Burdett, David [mailto:david.burdett@commerceone.com]
> Sent: Thursday, April 10, 2003 9:42 PM
> To: 'Cummins, Fred A'; Assaf Arkin; Burdett, David
> Cc: 'jdart@tibco.com'; public-ws-chor@w3.org
> Subject: Internal processes and/or external choreographies (was RE:
> Events and States ...
> 
> 
> Thanks ... but one thing we haven't nailed down yet is the 
> extent to which
> the scope of this group covers definition of languages to 
> define internal
> process definitions (as in WSCI and BPEL4WS) as well as external
> choreographies. I have been focusing on the latter but we 
> need to be clear
> what we are doing about the former.
> 
> For example we could have the following as requirements for 
> internal process
> definitions ...
> 
> "An internal process definition MUST be capable of defining 
> the sequence and
> rules by which software is executed within a 'Control Domain' 
> " ... Control
> domain has been defined/described/discussed earlier.
> 
> "An internal process definition MUST be capable of identifying the
> relationships and dependencies it has on an external choreography
> definition."
> 
> ... I am sure there are more, like internal process 
> definitions being Turing
> complete ...
> 
> Any thoughts chairs?
> 
> David
> 
> -----Original Message-----
> From: Cummins, Fred A [mailto:fred.cummins@eds.com]
> Sent: Thursday, April 10, 2003 5:38 PM
> To: Assaf Arkin; Burdett, David
> Cc: 'jdart@tibco.com'; public-ws-chor@w3.org
> Subject: RE: Events and States (was: timeouts & states (was: Abstract
> Bind able Choreography))
> 
> 
> David,
> 
> I'm not sure why I haven't received your message directly, but
> I like your linkage of state machine to process functionality.
> This provides a clean separation of the external choreography
> from the internal process.  We can then focus on how messages
> are exchanged between participants according to the state 
> transitions of their public state machines.
> 
> Fred
> 
> > -----Original Message-----
> > From: Assaf Arkin [mailto:arkin@intalio.com]
> > Sent: Thursday, April 10, 2003 7:17 PM
> > To: Burdett, David
> > Cc: 'jdart@tibco.com'; Cummins, Fred A; public-ws-chor@w3.org
> > Subject: Re: Events and States (was: timeouts & states 
> (was: Abstract
> > Bind able Choreography))
> > 
> > 
> > +1
> > 
> > arkin
> > 
> > Burdett, David wrote:
> > 
> > > >>>Very good questions. But what do you want (or perhaps more 
> > > importantly,
> > > need) it to do? As you say, a state machine is really a 
> > mechanism. What
> > > is the functional requirement?<<<
> > >
> > > I would put the functional requirements for which state 
> > machines are a 
> > > possible answer as follows:
> > >
> > > "An implementation of a process that is following a 
> > choreography MUST 
> > > be able to verify that the choreography is being followed 
> > correctly as 
> > > specified in the choreography definition."
> > >
> > > I would then have two further more closely defined but related 
> > > requirements of the products of this group ...
> > >
> > > "A choreography definition should be usable at Design Time 
> > to validate 
> > > that a process should be capable of carrying out a choreography 
> > > correctly as specified."
> > >
> > > "A choreography definition shoule be usable at Run Time 
> to validate 
> > > that a process is executing a choreography correctly as 
> specified".
> > >
> > > ... and finally one more ...
> > >
> > > "If a process detects that a choreography is not being followed 
> > > correctly, then the process SHOULD be able to use the 
> choreography 
> > > definition to identify exactly what went wrong."
> > >
> > > This last one means that you stand a better chance of 
> being able to 
> > > fix the problem when it occurs.
> > >
> > > Thoughts?
> > >
> > > David
> > >
> > >
> > > -----Original Message-----
> > > From: Jon Dart [mailto:jdart@tibco.com]
> > > Sent: Thursday, April 10, 2003 2:56 PM
> > > To: Cummins Fred A
> > > Cc: public-ws-chor@w3.org
> > > Subject: Re: Events and States (was: timeouts & states 
> > (was: Abstract
> > > Bindable Choreography))
> > >
> > >
> > >
> > > Cummins, Fred A wrote:
> > > > This raises questions about the scope of a choreography.  
> > When does
> > > > it end?  When a disconnect occurs?  When a particular business
> > > > transaction is completed?  When a relationship is terminated?
> > > > Maybe any of the above?
> > > >
> > > > Do the state machines provide the mechanism for nesting 
> > of component
> > > > choreographies?
> > >
> > > Very good questions. But what do you want (or perhaps more 
> > importantly,
> > > need) it to do? As you say, a state machine is really a 
> > mechanism. What
> > > is the functional requirement?
> > >
> > > At minimum, I would guess it is the ability to transition 
> > to a distinct
> > > state when a timeout occurs. This state could be the 
> > termination of the
> > > choreography (implying no more processing will occur). Or 
> > it could be an
> > > error state (implying there might be some warning given, or some
> > > recovery effort made, e.g. a retry - this assumes you are 
> > doing this at
> > > the application level and not in some lower-level 
> reliable messaging
> > > protocol). Certainly I can think of real-world examples 
> > where you'd need
> > > this functionality. This is something of a simplification 
> of earlier
> > > proposals. If we need something more complex, I'd like to see some
> > > rationale behind it.
> > >
> > > --Jon
> > >
> > 
> > 
> > -- 
> > "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 Thursday, 10 April 2003 22:43:36 UTC

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