Use of participants for scoping

In the current CDL specification (Web Services Choreography Description
Language Version 1.0, W3C Working Draft 27 April 2004) the word
'participant' is used consistently in the text as the thing that exchanges
information by exchanging messages (a described by the interaction elements)
with other such things.  However, are participant can consist of one or more
roles (which represent one or more classes of behaviour) and therefore it is
the 'Role' element that is used in the actual XML Choreography description
schema and instance documents thereof.
 
I suggest that a participant is defined as a set of one or more roles that
can share variable data by 'assignment' rather than message passing, and
that therefore a participant provides the scoping boundary for variable
information sharing.
 
If this change is agreed various parts of the specification may need to be
amended and I have not found all those places.  One place such place is 3rd
paragraph of  2.3 'Coupling Web Service participants' which currently reads:
 Within a Choreography, information is always exchanged between
Participants. 
 
This is arguably incorrect anyway as we definitely need a way of modelling
the passing of information between roles within a participant.  I suggest
amending to something like:
Within a Choreography, information is always exchanged by message passing
using Interaction elements between Participants, and by sharing Variables or
by assignment between Variables for information exchange between Roles
within a Participant. 
 
The alternative approach would be to confine variable scope to only being
that of a role and no wider at all and to use message passing (interaction)
between roles within a participant as well as between roles in different
participants.  However, this means that participant rightly figures strongly
as a modelling concept in the language model and text, but is not used or
useful in the language itself.
 
Best Regards     Tony
A M Fletcher
 
Cohesions  (TM)
 
Business transaction management software for application coordination
www.choreology.com <http://www.choreology.com/> 
 
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