Features and Properties

WSD Members,

Since starting, the WS-Choreo WG has been focused on requirements. It has
taken us some time to get there but we now have, we believe, a picture of
what we
expect from a WS Choreography language. In a similar manner to emerging WSDL
2.0,
we envisage a language with (at least) two levels. The abstract level will
define the
potential observable behaviors in terms of messages being exchanged,
sequencing 
constraints and other ordering and parallel composition rules. This level is

independent of deployment context, in the same way that abstract wsdl is.
The concrete 
level defines the deployment environment for an abstract choreography,
detailing 
the binding information to establish communication channels between
participants. 
This is similar to concrete WSDL. 

As a group we have spent time talking about the concrete level and have
reached several conclusions:

1. The group cannot assume there is a single stack on which to bind
choreographies. For example, there is no normative WS reliability protocol. 
This means that at some level each participating web service needs to
declare 
what protocols it supports and/or requires. This should be done at the 
concrete level.

2. It is unrealistic to expect that all participating web services in a
deployment will support the same protocols, and hence this should not be
done at a
global choreography layer. Therefore each participant will need to express
its
protocol support.

3. A language to express concrete binding information for a participating
web service is more general than a  choreography language and hence should 
not be dependant on it. It should a separable piece, and be usable without 
using the choreography language.

4. As a group we realize we have a lot of work to do on the main
choreography language, and would rather not be distracted with by defining 
a concrete binding language.

5. Complex negotiations between participants is not required for basic
choreographies. Therefore the group feels that, at this stage, it only 
requires a language to express endpoint capabilities. 
 
The group is aware of work within the WSD WG, in particular the features and
properties
framework. The Choreo group believes that features and properties
will provide an adequate foundation for defining concrete binding
information 
for each participating web service. It is related to a single WSDL
definition, and  
thus could meet our requirements, outlined above. Having the piece of work 
be part of WSDL 2.0 will save the Choreo group at lot of time. 
The group realizes that features  and properties is an evolving piece of
work,
and we would be very happy to work with the WSD WG to refine it, if
necessary. 

We look forward to discussing this with you,

Martin Chapman and Steve Ross- Talbot, on behalf of the WS Choreography WG.

_________________________________________________________________
Martin Chapman                                 
Consulting Member of Technical Staff           
Oracle                                        
P: +353 87 687 6654                           
e: martin.chapman@oracle.com

Received on Tuesday, 20 January 2004 17:10:00 UTC