Re: [wsrp][interfaces]: Actions vs. Events

[Dave Clegg <davec@sybase.com>]

If the portal is presenting 2 or more different views of the same service
instance then 'getmarkup' would need some input parameter indicating what
view the markup should be for. This may be preferable to defining different
getXXXMarkup methods for every conceivable view type.
The action concept seems important to me. The portal developer is the one
who is mixing and matching WSRP services into a meaningful application, and
that is where the higher-level logic of propagating events among participating
portlets needs to be handled. Unless the state-changing "action" method is
temporally separated from getmarkup there is no opportunity for the event
propagation to finish propagating. We should not assume that the service
provider is handling all event notification and processing (and we might
argue that it is undesireable for it to be required to do any).
As an efficiency, we might allow for the simpler performActionGetMarkup that
is essitially a 1-phase operation when the portal somehow knows that there
will be no event propagation associated with the current action that could
affect the markup returned, thus removing a round-trip to the service.

dave

Michael Freedman wrote:
> 3CBB2990.55A0C3CB@oracle.com">
> Each of these seem to imply that markup is (ultimately) returned.  If this is
> the case then why isn't there a single method for all calls that return markup?
> If we want to name that  "actions" so be it.  But couldn't we also name it
> "getmarkup"?  In either case the "action" or operation the producer performs is
> defined by a (collection) of parameters passed in that define the type/form of
> the markup to be produced.
>       -Mike-
>
> Alan Kropp wrote:
>
> > Mike, I would agree that the concept of an "action" for a portlet with a
> > single view (e.g., a counter or timer, something which does not expect user
> > input) is really overkill.  The portlet will render its one default, or
> > "main", view in response to the portal refreshing or instantiating the
> > containing page.
> >
> > Where I think actions have merit is in two areas:
> >
> > 1.  The portlet supports a customization or "edit" view.  The end user would
> > specifically invoke the "Display Edit View" action by clicking an
> > appropriate link or button on the portlet's main view, or perhaps on the
> > frame surrounding it.  The corresponding action defined on the portlet would
> > be "getEditView" or something like that.  The portlet would respond with the
> > markup for the edit view, and the portal would accordingly redraw that part
> > of the page.  In fact, this may be an example of a standard portlet action
> > which WSRP portlets may implement.
> >
> > 2. 
> >  The portlet supports a series of application-specific views, perhaps in
> > a step-by-step or "wizard"-lilke flow.  Each view has a control linking it
> > to the next view in the sequence.  The transition from view to view could be
> > handled on the portlet side by a "getNextView" action, which examines the
> > associated parameters to determine which application view to fetch.
> >
> > Alan
> >
> > -----Original Message-----
> > From: Michael Freedman [mailto:Michael.Freedman@oracle.com]
> > Sent: Monday, April 15, 2002 11:26 AM
> > To: Carsten Leue
> > Cc: wsrp@lists.oasis-open.org
> > Subject: Re: [wsrp][interfaces]: Actions vs. Events
> >
> > Carsten,
> >     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
> > essential
> > .
> > 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
> > provide
> > 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
> > followed
> > by a render call.  This would seem to lessen the desirability of the
> > abstraction.  Can
> > you motivate "actions" more?
> >      -Mike-
> >
> > Carsten Leue wrote:
> >
> > > 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
> > >
> > >   ------------------------------------------------------------------------
> > >                                  Name:
> > >  Action vs Event.zip
> > >    Action vs Event.zip           Type: Winzip32 File
> > >                       
> > (application/x-zip-compressed)
> > >                              Encoding: BASE64
> > >                       Download Status: Not downloaded with message
> > >                         
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