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

RE: More requirement

From: Jean-Jacques Dubray <jjd@eigner.com>
Date: Wed, 18 Jun 2003 08:40:10 -0400
To: "'Yaron Y. Goland'" <ygoland@bea.com>
Cc: "'WS Chor Public'" <public-ws-chor@w3.org>
Message-ID: <006201c33596$d42e8190$2278050a@JJD>

If two parties believe that the choreography is in a different state,
one can have many surprises about the outcome of this choreography. A
choreography is a state machine (in the mathematical sense) and as such
is always in a given state. The language must be unambiguous about the
different state. It is merely the exchange of a message that changes the
state of the choreography. However, it is a very peculiar state machine,
since it has no run-time associated with it that keeps ITS state.  Its
state is rather "spread" over n parties, which are all represented by
their individual state machines participating in the choreography. As
you can imagine if these state machines gets out of synch only the most
catastrophic results can be expected.

Cheers,

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: Yaron Y. Goland [mailto:ygoland@bea.com]
>>Sent: Dienstag, 17. Juni 2003 13:05
>>To: Jean-Jacques Dubray; 'WS Chor Public'
>>Subject: RE: More requirement
>>
>>I have to admit that the term 'choreography state synchronization
>>mechanism'
>>makes me really nervous only because it is so broad that it could
>>potentially mean anything. But let's adopt your proposed new language
>>anyway
>>and when we do the full requirements review we can do a pass to look
for
>>phrases such as that one and make sure they are used in a consistent
and
>>well defined manner throughout the requirements.
>>
>>		Yaron
>>
>>> -----Original Message-----
>>> From: Jean-Jacques Dubray [mailto:jjd@eigner.com]
>>> Sent: Wednesday, June 11, 2003 12:44 PM
>>> To: 'Yaron Y. Goland'; 'Jean-Jacques Dubray'; 'WS Chor Public'
>>> Subject: RE: More requirement
>>>
>>>
>>> Yaron:
>>>
>>> >>
>>> >>BPSS has chosen one of a number of possible MEPs and each MEP has
its
>>> own
>>> >>benefits and drawbacks that I don't believe this group needs to
>>> address.
>>> >>In
>>> >>fact I expect that each industry will pick the MEPs that best meet
>>> their
>>> >>functional and legal requirements. Therefore I would propose that
our
>>> job
>>> >>is
>>> >>to enable the creation of such MEPs rather than specifying exactly
>>> what
>>> >>they
>>> >>are.
>>> [JJ] +1
>>> >>
>>> >>As such I would propose rewriting Jean-Jacques' proposed
requirement
>>> as:
>>> >>
>>> >>The WS-Chor message sequence description language MUST take into
>>> >>consideration the need to manage signals where a signal is defined
as
>>> an
>>> >>application level processing error that is expressed as a message
>>> visible
>>> >>by
>>> >>other partners in the choreography.
>>> [JJ] I am not sure I would translate it this way. Signals are not
just
>>> application level processing error messages. You may also have
"message
>>> format errors" that could be trapped above the system of record.
>>>
>>> I would suggest:
>>>
>>> >>The WS-Chor message sequence description language MUST take into
>>> >>consideration the need to manage signals where a signal is defined
as
>>> <a choreography state synchronization mechanism> that is expressed
as a
>>> <standard> message visible
>>> >>by
>>> >>other partners in the choreography.
>>>
>>>
>>> >>
>>> >>> -----Original Message-----
>>> >>> From: public-ws-chor-request@w3.org
>>> >>> [mailto:public-ws-chor-request@w3.org]On Behalf Of Jean-Jacques
>>> Dubray
>>> >>> Sent: Thursday, June 05, 2003 2:51 AM
>>> >>> To: 'WS Chor Public'
>>> >>> Subject: More requirement
>>> >>>
>>> >>>
>>> >>>
>>> >>> I would like to add another requirement:
>>> >>>
>>> >>> The WSC-Languange MUST provide specific Message Exchange Pattern
>>> >>> templates that establish a reliable state of the WSC-instance
when
>>> >>> needed.
>>> >>>
>>> >>> This requirement is essential since RM itself is not enough to
>>> guaranty
>>> >>> that the state of the choreography is identically represented in
>>> each
>>> >>> party. For instance a party sends a message with an incorrect
>>> format. If
>>> >>> we have RM only, then the state of the collaboration says that
the
>>> >>> message got there, so the choreography should proceed as normal.
>>> >>> However, if this is a request, the responding party cannot send
the
>>> >>> response since the message was structurally incorrect.
>>> >>>
>>> >>> Unless the WSC-definition specifies that at this point the
>>> responding
>>> >>> party can send a "INVALID MESSAGE" response, we get into a
deadlock
>>> >>> (requesting party waiting for response, responding party unable
to
>>> >>> respond).
>>> >>>
>>> >>> A similar deadlock can happen when the message is structurally
>>> valid,
>>> >>> but cannot be processed by the corresponding system of record
(that
>>> is
>>> >>> in charge of producing the response).
>>> >>>
>>> >>> Providing MEP-templates would greatly simply the work of the
>>> designers
>>> >>> by establishing clear patterns, with standard error messages
that
>>> can be
>>> >>> used over and over by anybody.
>>> >>>
>>> >>> This approach also offloads the business logic of the
application/or
>>> >>> process engine to deal with "protocol" levels. Can you imagine
the
>>> >>> simplification for the Orchestration/Process Definition-instance
if
>>> >>> these concepts are implied rather than explicitly handled by the
>>> process
>>> >>> instance?
>>> >>>
>>> >>> See also this article:
>>> >>> http://www.looselycoupled.com/stories/2003/message-infr0528.html
>>> >>>
>>> >>> Of course most people would have recognized the BPSS business
>>> >>> transaction protocol, that itself has its root in prior work at
RN
>>> and
>>> >>> UN/CEFACT. I think that generalizing this idea would be helpful.
>>> >>>
>>> >>> Cheers,
>>> >>>
>>> >>> Jean-Jacques Dubray____________________
>>> >>> Chief Architect
>>> >>> Eigner  Precision Lifecycle Management
>>> >>> 200 Fifth Avenue
>>> >>> Waltham, MA 02451
>>> >>> 781-472-6317
>>> >>> jjd@eigner.com
>>> >>> www.eigner.com
>>> >>>
>>> >>>
>>> >>>
>>> >>>
>>> >>>
>>>
>>>
Received on Wednesday, 18 June 2003 08:41:10 GMT

This archive was generated by hypermail 2.2.0+W3C-0.50 : Saturday, 18 December 2010 01:00:21 GMT