RE: Partial executability/ determinism of a Chor description la nguage

I think that "machine execution" can only take place inside a process
running at an individual role (e.g. a buyer or a seller). This means that
the "decision expression" is internal to that process. What's external is
the data that goes over the wire, ie. the message content. Each piece of the
data should have a well defined semantic. Again this separating how the
decision is made from recording and communicating the results of the
decision.
 
David

-----Original Message-----
From: Ricky Ho [mailto:riho@cisco.com]
Sent: Friday, May 30, 2003 8:27 AM
To: Burdett, David; Yaron Y. Goland; public-ws-chor@w3.org
Subject: RE: Partial executability/ determinism of a Chor description la
nguage


I don't disagree with you about putting an extra level of indirection.  What
I'm focusing here is where that decision expression is ultimately "machine
executable" at the Choreography level.  I think that should be OK which is
different from Yaron's original point.

Rgds, Ricky

At 09:45 PM 5/29/2003 -0700, Burdett, David wrote:


Ricky
 
I think you are really defining the semantics and content of a particular
interchange. In this case, the results of your decision process would
probably end up as data content inside a PO Response document. The fact that
this information is included is a decision of the message/protocol designer.
 
Note however that you could have the identical choreography (i.e Buyer sends
a PO, Seller returns a PO Response) without including this information.
 
This is a good example of why you want to separate the choreography
definition from the detailed message content definitions.
 
David 


-----Original Message----- 

From: Ricky Ho [ mailto:riho@cisco.com <mailto:riho@cisco.com> ] 

Sent: Wednesday, May 28, 2003 12:18 AM 

To: Yaron Y. Goland; public-ws-chor@w3.org 

Subject: RE: Partial executability/ determinism of a Chor description
language



I think there are 2 kinds of decision logic ...



1) Private decision that I want to keep secret 

E.g. If you send me a PO, I will either accept it or reject it.  But I don't
want to share with you how I decide.



2) Public decision that I want my partners to know about 

E.g. If you send me a PO, I want to tell you that I will reject your PO
message if you don't have a valid signature.



I think WS-Chor should cover the later but not the former.  But I don't
think expressing an XPATH necessary mean exposing private decision.  You may
intentionally want to expose your decision criteria to your partners so they
don't waste time to prepare something invalid.



Best regards, 

Ricky



At 09:11 PM 5/27/2003 -0400, Yaron Y. Goland wrote: 



My personal preference is that nothing be said in the cDl about how the
message is to be processed. E.g. nothing is ever said about the contents of
the message and decisions made on those contents. This is exactly what BPEL
in general and BPEL abstract processes in particular are intended for. They
provide direct insight into how a participant makes a decision at whatever
level of detail one cares to share. 



The cDl on the other hand describes just the global behavior without insight
into a particular process. That is its key distinction with regards to BPEL.
If this group chooses to go down the path of providing the type of message
based execution decision described below inside of the cDl then the working
group will be taking a position that puts it into direct competition with
BPEL. 



There is nothing in the group's charter that says 'thou shalt avoid
competing with BPEL' and perhaps our best technical needs will be met by
such a competition. I personally do not believe so and have explained my
reasoning in my use case/requirements document. But if we do decide to
provide insight into the internals of a process's execution we should do so
with a clear understanding that we are talking a position in direct
competition with BPEL. 



    Thanks, 



        Yaron 

-----Original Message----- 

From: public-ws-chor-request@w3.org [
mailto:public-ws-chor-request@w3.org]On
<mailto:public-ws-chor-request@w3.org%5DOn>  Behalf Of Fletcher, Tony 

Sent: Thursday, May 22, 2003 2:41 AM 

To: public-ws-chor@w3.org 

Subject: Partial executability/ determinism of a Chor description language 

Dear Colleagues, 

I would like to clarify in my own mind and continue a discussion o the
degree to which a Choreography description language (CDL) is deterministic
or 'executable'.  I think this issue links to previous threads on the use of
information from messages, or not. 

I think we all agree that a CDL will only give a very partial description of
the behaviour of any 'entity' playing a particular role (and that you do
need a full programming language such as Java or C#  for any sort of
'complete' description. 

However, consider the following: 

Role A sends message 1 to role B 

Role B replies with message 2 to role A 

At this point there may now be say three different messages that A could
next send to B according to the CDL instance and given no other information.


Now suppose that message 1 was an order message and message 2 an order
response with a critical information field that says 'accept' or 'reject'. 

The CDL could now say that role A can examine the incoming message 2 extract
the semantic accept or reject and if reject then send message 3 else send
message 4 or message 5 (means of determining which is not shown in this CDL
instance, but would be in the CPL for that role). 

Without being dependent on the precise syntax of messages, only some of the
semantic elements, I think that some people in this group would like the
above behaviour to be supported by the WS-Chor language and thus support for
this behaviour to be a requirement. 

Others seem to be arguing for no dependence on message content at all -
perhaps just the name of the message received(?).  Can we reach an amicable
consensus? 

Best Regards     Tony 

A M Fletcher 

Cohesions 1.0 (TM) 

Business transaction management software for application coordination 

Choreology Ltd., 13 Austin Friars, London EC2N 2JX     UK 

Tel: +44 (0) 20 76701787   Fax: +44 (0) 20 7670 1785  Mobile: +44 (0) 7801
948219 

tony.fletcher@choreology.com <mailto:tony.fletcher@choreology.com>
(Home: amfletcher@iee.org)