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

Ricky
 
I agree that the *decision* should not be recorded in the choreography. On
the other hand I think that the states that result from making a decision
should. This allows separation of the what (the states) from the how (the
decision).
 
So, in the choreography, you would need two states, say: OrderAccepted, and
OrderRejected, as that is (probably) all that is needed to define the
choreography.
 
On the other hand, if you want to put additional data in the message to
explain *why* the order was rejected, for example, then you can do this.
However it does not affect the basic choreography.
 
However you could imagine the following variation of where the outcome was
three states: OrderAccepted, OrderRejected:OutOfStock, and
OrderRejected:SubstituteOffered.
 
The idea is that in this particular choreography a seller when rejecting an
order can offer a substitute instead. It is then up to the buyer to accept
(or reject) the substitution so there needs to be additional messages.
 
Again the detail of the substitution only needs to go in the content of the
message.
 
Bottom line, I think it is much clearer if you think about the states that
arise and to define what messages get exchanged when a particular state (or
combination of states) arise. That way, you can keep private the decision
process  you make before deciding on how to change state.
 
David

-----Original Message-----
From: Ricky Ho [mailto:riho@cisco.com]
Sent: Friday, May 30, 2003 8:23 AM
To: Burdett, David; public-ws-chor@w3.org
Subject: RE: Partial executability/ determinism of a Chor description
language


Yaron's original point is that there shouldn't be any decision being exposed
in choreography as XPATH.  I'm just thinking about some counter examples.

We probably talking about different things.  What you say is an agree-upon
error code so that after the order is rejected, the buyer know the reason
(in other words, the buyer knows the seller's private decision after the
fact.  This is different from my example, what I say is the seller want to
declare his decision upfront so that everyone will know before they send the
message.  Isn't this a valid use case ?

Rgds, Ricky

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


Following on from this, in practice you would need to have error codes in
the return message that included one for "badlist" country. To realize
interoperability, the error codes that could be present in the message data
should be published in advance. In this case the sender should already know
that orders from a badlist country would not be accepted.
 
I don't see what this has to do with choreography ... or am I missing
something.
 
David 


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

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

Sent: Wednesday, May 28, 2003 4:55 PM 

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

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



Sorry if I give a bad example.  I just want to show in some case you
intentionally want to share your decision to the public.  How about this one
? 

I want to share every buyer my decision that if the destination address is a
badlist country, I won't accept the PO.



Rgds, Ricky



At 09:53 AM 5/28/2003 -0400, Yaron Y. Goland wrote: 



Isn't the decision to require the use of a signature a configuration
decision and therefore should be covered with a configuration mechanism and
not in the high level workflow logic? 

-----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 Ricky Ho 

Sent: Wednesday, May 28, 2003 3:18 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>
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