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Subject: RE: [wsrp][interfaces]: Actions vs. Events

A simple scenario that may help clarify why actions and events should be
separate from markup.
1) user submits action to portal initiating action/event phase,
2) portal submits action to portlet 
3) action generates event consumed by another portlet,
4) second portlet generates event that is consumed by first portlet
5) action/event handling phase of portal is finished
6) portal calls getMarkup to retrieve markup corresponding to current state
of first portlet.

The user is not interested in any of the intermediate states or markup that
might be generated as a result of these states, only the markup
corresponding to the final state of the portlet.


-----Original Message-----
From: Michael Freedman [mailto:Michael.Freedman@oracle.com]
Sent: Monday, April 15, 2002 2:26 PM
To: Carsten Leue
Cc: wsrp@lists.oasis-open.org
Subject: Re: [wsrp][interfaces]: Actions vs. Events

    Thanks for this write-up.  I better understand the differences between
actions and
events.  What I don't understand is why action handling is absolutely
Web/servlet programmers have gotten along fine without this abstraction for
a long time
now.  And I don't see anything (yet) in how you have defined actions that
benefit over and above handling the action as part of a render/getmarkup.
And given
our performance concerns I imagine actions will either be defined to return
markup --
i.e. they are another form of getmarkup/render.  Or "actions" will be
modeled in the
producer as part of a producer side portlet container -- i.e. the portal
makes a render
call but the producer side portlet container breaks this into an action call
by a render call.  This would seem to lessen the desirability of the
abstraction.  Can
you motivate "actions" more?

Carsten Leue wrote:

> Hi - as promised in the interface call here is a definition of what I
> define as "actions" and "events". We might use this as a starting point
> 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
> 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
> 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
> the services). Events are not directly represented in the markup but
> 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
> 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
> 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 B÷blingen , Germany
> Tel.: +49-7031-16-4603, Fax: +49-7031-16-4401
>   ------------------------------------------------------------------------
>                                  Name: Action vs Event.zip
>    Action vs Event.zip           Type: Winzip32 File
>                              Encoding: BASE64
>                       Download Status: Not downloaded with message

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