Title:     WS-Messaging System
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Airavata WS-Messenger is a Web Services-based Messaging System for Service-Oriented Computing and is
an implementation of [WS-Notification][wsn] and [WS-Eventing][wse] specifications. The message format 
can be automatically converted between the two specifications. The subscription request type
(Ws-Notification or WS-Eventing) for a listener determines the message format that the notification 
consumer will receive. If WS-Notification subscription request is received by the broker, it will 
send WS-Notification messages to the listener. Similarly, if WS-Eventing subscription is received 
by the broker, the broker will produce WS-Eventing messages for that listener. The publisher can 
publish messages in either format. The consumers will recieve messages in the format they subscribed 
irrespective of the format the message is published.

The following figure illustrates the high level overview of the WS-Messenger 
![WS Messenger Overview](/documentation/messenger/messenger-overview.png "WS Messenger Overview")

## WS-Messenger Modules 
The WS-Messenger has three major modules.

1. Message Broker: The broker is a traditional notification broker responsible for recieving 
subscriptions and events published. 
2. Messenger: The messenger responsibility is to delivar messages to all the subscribers and 
message boxes. 
3. Message Box: provide a web service interface for subscribers behind the firewalls. This service
stores notification messages until the subscribers pull messages where the firefall blocks a push.
This module also assists in reliable delivary otherwise lost due to network and client glitchs.

  [wsn]:  http://www.oasis-open.org/committees/wsn/
  [wse]:  http://www.w3.org/Submission/WS-Eventing/