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Subject: RE: [wsrp][interfaces]: Actions vs. Events
This is what I had in mind as well. If different producer want to communicate directly, they can do this regardless of WSRP. What is needed is some variation of a publish/subscribe (with data) mechanism managed by the consumer. Yossi. -----Original Message----- From: PAVLIK,GREGORY (HP-NewJersey,ex2) [mailto:gregory_pavlik@hp.com] Sent: Monday, April 15, 2002 10:20 PM To: 'Alan Kropp'; 'Carsten Leue'; wsrp@lists.oasis-open.org Subject: RE: [wsrp][interfaces]: Actions vs. Events that would be preferrable. -----Original Message----- From: Alan Kropp [mailto:akropp@epicentric.com] Sent: Monday, April 15, 2002 3:16 PM To: 'Carsten Leue'; wsrp@lists.oasis-open.org Subject: RE: [wsrp][interfaces]: Actions vs. Events Hi Carsten, On the subject of event handling, could we simplify the scenario a bit by allowing the portal to act as the intermediary in event propagation? I'm thinking of a publish/subscribe model (somewhat like JMS), in portlets which support events "publish" those events to the portal, and portlets which consume events inform the portal by subscribing for those event types. The portal acts as the intermediary, and neither event producers or consumers need know specifically about each other. Alan -----Original Message----- From: Carsten Leue [mailto:cleue@de.ibm.com] Sent: Monday, April 15, 2002 3:49 AM To: wsrp@lists.oasis-open.org Subject: [wsrp][interfaces]: Actions vs. Events Hi - as promised in the interface call here is a definition of what I would define as "actions" and "events". We might use this as a starting point for the further discussion. Both actions and events are notifications for a WSRP service. 1. Action: Actions are notifications that are triggered by the user. During the creation of markup the service encodes special URLs in the markup and associates data to them. The aggregator may need to rewrite the URLs to make them appear as links and redirect them to the aggregator. The end user can click on the links to trigger such an action. The aggregator then intercepts this and issues a call to the action handler defined in the WSRP interface together with the data the service encoded in the markup. As a reaction to this action the service may modify its state an regenerate its markup. The following points are important in this scenario: - the set of possible actions is defined by the server by embedding them in the markup - the end user triggers the actions - there is only one consumer of an action: the service that embedded the action into the markup 2. Event: Events are launched programatically by components (the aggregator or one of the services). Events are not directly represented in the markup but issued by the components depending on their state (could be a timer, a system event or as a reaction to an action). Events can either be broadcast to all services or to a set of registered services. The following points are important in this scenario: - the set of receivers of events (listeners) is dynamic - if a service fires an event it needs to connect to the listeners. This might not always be possible due to firewall restrictions - i becomes possible to halt the system by (accidentally) introducing cycles in the event propagation Following this definition event handling is much more complex and error prone than action handling and the two serve different purposes: user interaction and notification. 3. Relationship to WSRP From my point of view we should clearly distinguish between action handling and event handling in WSRP. Event handling easily becomes very complex and is not always required to support portal/portlet interaction. Maybe we should separate event handling out into an optional interface. My proposition would be to reuse the WSIA event handling interfaces for this but leave it up to the service to support this feature. Action handling however is abosultely essential for user interaction. For this reason it makes sense for me to include this functionality into the base WSRP interface. I added a PDF document to further clarify the distinction graphically. (See attached file: Action vs Event.zip) Best regards Carsten Leue ------- Dr. Carsten Leue Dept.8288, IBM Laboratory Böblingen , Germany Tel.: +49-7031-16-4603, Fax: +49-7031-16-4401 ---------------------------------------------------------------- To subscribe or unsubscribe from this elist use the subscription manager: <http://lists.oasis-open.org/ob/adm.pl> ---------------------------------------------------------------- To subscribe or unsubscribe from this elist use the subscription manager: <http://lists.oasis-open.org/ob/adm.pl>
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