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



I agree that we should defer event handling until we have sorted out the
more basic things that we need to define.

However, I think we should gather and consolidate the thoughts and options
that were discussed in this mail thread in a document to which we can get
back later.

Volunteers to do a brief writeup ?

Best regards,

Thomas


Jeff Broberg <jbroberg@silverstream.com> on 04/22/2002 07:21:54 PM

Please respond to jbroberg@silverstream.com

To:    Rich Thompson/Watson/IBM@IBMUS, wsrp@lists.oasis-open.org
cc:
Subject:    RE: [wsrp][interfaces]: Actions vs. Events



Rich - I have taken the action/event defs and added them to the glossary -
jcb

I also agree with Rich that events while important, appear to be a slippery
slope, and I would also suggest moving them into a follow on version of the
spec.

-----Original Message-----
From: Rich Thompson [mailto:richt2@us.ibm.com]
Sent: Monday, April 22, 2002 12:33 PM
To: wsrp@lists.oasis-open.org
Subject: RE: [wsrp][interfaces]: Actions vs. Events



I'm not sure limiting event types to those published in meta-data would
suffice. Consider the case of a Producer that provides a redirection to
other services that it has been instructed to instantiate (or maybe just
"contain"). The events such a Producer would publish are dependent on the
indirect providers and therefore can not be published statically. An
example of such a Producer could be a portal publishing a set of portlets
as a WSRP service for other portals to consume.

While I consider events to a important to both the WSIA and WSRP standards,
I would suggest not pushing them into the first versions of the standards
as the WSDL layer of the web services stack has these poorly defined now
and there are efforts to clean up that portion of the WSDL spec.

Also, unless I missed it, I don't think I saw the terms action and event
being crisply defined. My suggestion:
      Action - A request to a Producer to execute some functionality.
      Event - A notice from a Producer that some logical transition has
occurred.




                      Jeff Broberg
                      <jbroberg@silvers        To:       "Tamari, Yossi"
<yossi.tamari@sapportals.com>,
                      tream.com>                wsrp@lists.oasis-open.org
                                               cc:
                      04/22/2002 11:40         Subject:  RE:
[wsrp][interfaces]: Actions vs. Events
                      AM
                      Please respond to
                      jbroberg





my mistake, i meant it in the context of actions not events.

-----Original Message-----
From: Tamari, Yossi [mailto:yossi.tamari@sapportals.com]
Sent: Monday, April 22, 2002 11:27 AM
To: 'wsrp@lists.oasis-open.org'
Subject: RE: [wsrp][interfaces]: Actions vs. Events


I do not know if I agree on this, since events are not generated by the
user, but by other providers (in the context of the user).
Anyway, if a provider does not wish to process a certain event in a certain
context, it can ignore the event in runtime.
I think that the overhead of implementing dynamic events may be bigger than
the overhead of having ignored events.

             Yossi.

-----Original Message-----
From: Jeff Broberg [mailto:jbroberg@silverstream.com]
Sent: Monday, April 22, 2002 6:22 PM
To: Tamari, Yossi; wsrp@lists.oasis-open.org
Subject: RE: [wsrp][interfaces]: Actions vs. Events


I can imagine a scenario where the events that a provider allows for a
particular user is context based, so that one individual may be able to
perform some type of action while another can't.  So we could define the
availalbe events in the metadata, but we may have to also allow this info
to
be dynamically generated and discovered.

jeff

-----Original Message-----
From: Tamari, Yossi [mailto:yossi.tamari@sapportals.com]
Sent: Monday, April 22, 2002 11:01 AM
To: wsrp@lists.oasis-open.org
Subject: RE: [wsrp][interfaces]: Actions vs. Events


My take on the registration issue is that the provider should include the
list of events/properties that it wants to subscribe to in its metadata.
It seems to me like this list does not need to be dynamic since in order to
process more events, more code needs to be written in the provider.

The place were loops may actually happen is when provider A raises event X,
which causes provider B to raise event Y, which causes provider A to raise
event X again (for example). There are different algorithms that can
prevent
this, and maybe we should leave this to the implementing portal. We could
define that the same event can not be fired by the same provider more then
once per request, and that the consumer is not required to continue
processing events if the chain is deeper than some constant number. I would
like to hear other suggestions to solving this problem.

             Yossi.

-----Original Message-----
From: Carsten Leue [mailto:cleue@de.ibm.com]
Sent: Monday, April 22, 2002 5:43 PM
To: Tamari, Yossi
Cc: wsrp@lists.oasis-open.org
Subject: RE: [wsrp][interfaces]: Actions vs. Events


I think that this would be a good solution for events to decouple the
portlets and solve the problems that the portlets might not "see" each
other through the firewalls. Furthermore it take the complexity of managing
listeners away from the services to the portal. I still see a semantic
difference between actions and events but maybe we can unify that. Some
open issues are from my point of view:

- visibility: per definition the portal has access to the service (e.g.
though a firewall). The same is not necessary true for the service that may
be shielded from directly accessing the portal. If we unify actions and
event we need
      - a way for the services to register/unregister themselves as
listeners passively without initiating a communication to the portal (e.g.
in the return values for the markup call)
      - is it also possible to trigger events passively?

- chaining: a portlet that has been integrated in a portal might be
republished and reintegrated by another portal
      - register/unregister requests for listeneres need to be delegated to
both portals
      - how can loops be avoided in such cases?


Best regards
Carsten Leue

-------
Dr. Carsten Leue
Dept.8288, IBM Laboratory B÷blingen , Germany
Tel.: +49-7031-16-4603, Fax: +49-7031-16-4401



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|         |           "Tamari, Yossi"   |
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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 B÷blingen , Germany
Tel.: +49-7031-16-4603, Fax: +49-7031-16-4401

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