Application data scenario (RE: [ws-caf] Context example assignments)

Here is my example use case using WS-Context for 
providing state of business process/activity.

 

Every business process or activity is performed by one 
or more participants usually representing individual systems or components in 
the enterprise which are involved in the activity. When the activity starts all 
its participants are in an initial state. The state of the participant changes 
based on the messages received from other participants in the scope of the 
activity. Let's define the state of the business activity as a sum of all 
messages exchanged in the activity scope among its participants. Anyone is able 
to determine the current activity state by looking at the messages exchanged 
during the activity assuming the he or she knows the initial state of the 
activity participants.

 

One possible way to capture the messages exchanged 
among participants during the activity is to install an intermediary which will 
mediate all the communication among activity participants. The activity state 
keeping intermediary will make the content of the messages available to the 
participants of the activity. The participants, which are aware of the activity 
state keeping intermediary would be able to interact directly with it and would 
be able to augment the activity state directly.

 

If all participant would be aware of that intermediary 
and would interact solely with it, the result would be very similar to the 
classical space-based programming model (as we know for example from Linda, 
T-Spaces or JavaSpaces). The state would be automatically stored on the 
intermediary and participants will never talk to each other directly. This model 
has many advantages over classical RPC-like systems, because it makes the 
participants more loosely coupled. In fact, only the data format of the 
shared state has to be negotiated and often even this can be partially overcome 
by using transformations of the state content customized for individual 
participants.

 

In reality, not all participants would be aware of the 
state keeping intermediary, often existing services and systems would be 
participants of the activity and it would be problematic to make them aware of 
the activity state. Therefore we would need to integrate both state-aware and 
state-unaware participants. The WS-Context specification seems to be ideal for 
propagating activity state identification to the existing participants (assuming 
that they would understand WS-Context spec). Using the WS-Context, the state 
keeping intermediary would be able to place the message to the right 
activity state storage according the the context ID inside the WS-Context 
header. Information from the WS-Context header can be used by state-aware 
participants to augment the state directly. This would require, that a 
resolvable identification of the state keeper would be stored in the header 
additionally with other state-access related data.

 

The state keeping intermediary would take advantage of 
WS-Context "activity start" and "activity end" events to manage the activity 
state in a proper way.

 

Finally, the management tools can use state-keeping 
intermediary to access, monitor and influence the complete state of the 
activity in a single place and can use WS-Context to address and manipulate the 
activity state.

 

In my opinion, WS-Context would nicely fit in this use 
case to propagate activity state identification to web services via regular SOAP 
messages and to allow them to leverage this information by interacting directly 
with the state content.

 

--Jan

  

  
  From: Newcomer, Eric 
  [mailto:] 
Sent: Thursday, December 11, 2003 
  9:16 PM
To: ws-caf
Subject: [ws-caf] Context example 
  assignments 

  

  
Hi,

  
 

  
For Monday's 
  concall it would be great to have some of the context examples circulated to 
  the email list far enough in advance to be able to discuss them on the 
  call.

  
 

  
In no particular 
  order:

  
 

  
-- User Context 
  example, Jan Alexander

  
-- Security 
  context example, Eric Yuan

  
-- 
  Database/File/Device example, Eric Newcomer

  
-- Cluster group 
  membership example, Mark Little

  
-- Session state 
  example, Greg Pavlik

  
 

  
I think that's it, 
  someone let me know if I've forgotten to include them.  Apologies for the 
  delay in getting the reminder out.

  
 

  
Eric        
  

  
 

  
 

  
 

  
 

  
Eric Newcomer
Chief Technology Officer


  
-------------------------------------------------------
IONA 
  Technologies
200 West Street Waltham, MA 02451 USA
Tel: (781) 
  902-8366
Fax: (781) 
  902-8009
-------------------------------------------------------
Making 
  Software Work Together TM