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Subject: RE: [wsrp][interfaces]: Actions vs. Events
-----Original Message-----
From: Rich Thompson [mailto:richt2@us.ibm.com]
Sent: Thursday, April 25, 2002 8:13 AM
To: WSRP
Subject: RE: [wsrp][interfaces]: Actions vs. Events
I would disagree that an action is a notification that the service's state
has changed. The invoker has no means of knowing that any state change has
occurred ... an example where it hasn't would be a button pressed that just
results in an action being invoked. At the point of the action being
invoked, there has been not a state change for the service (though there
likely will be as a result of the action's execution). That is why I
proposed an action definition that centers around it being a request for
the service to do something ... there may be state changes involved both
before and after the action is invoked, but they aren't central to defining
what an action is.
Jeff Broberg
<jbroberg@silvers To: Michael Freedman <Michael.Freedman@oracle.com>, Rich
tream.com> Thompson/Watson/IBM@IBMUS, WSRP <wsrp@lists.oasis-open.org>
cc: Denise Dean <ddean@silverstream.com>
04/24/2002 09:37 Subject: RE: [wsrp][interfaces]: Actions vs. Events
PM
Please respond to
jbroberg
i have updated the glossary for these modified terms and will be sending
the latest version out to the group either wed or thu of this week.jeff
-----Original Message-----
From: Michael Freedman [mailto:Michael.Freedman@oracle.com]
Sent: Wednesday, April 24, 2002 6:03 PM
To: Rich Thompson; WSRP
Subject: Re: [wsrp][interfaces]: Actions vs. EventsRich,
I like your idea that given we have many descriptions on the table
we should see if we can solidify the discussion by first defining
terms. Once we have a good definition of terms we can then more
effectively discuss requirements. I think your definitions are a good
start but might be improved if made more concise. What do you think
of the following definitions:
Action: a notification that your state has changed.
There is only one recipient of an action. This recipient is
identified in the action request. For example, a portlet
encodes an action in the URI of its form's "Submit" button.
This URI (the action request) explicitly targets the receiver
(this portlet instance).
Event: a notification that some state in the system (that you are
interested in) has changed.
There may be 0 to many recipients of an event. The recipient
of an event is not identified in the event request. Rather,
event recipients are managed (by an event manager). An event
request is sent to/via the event manager which then dispatches
the event notification to interested parties. I.e. the major
differences between an action an event is that event recipients
are anonymous and a single event may be dispatched to many
portlets.
I believe the above clearly defines the differences between actions
and events from the point of view of the invoker. However it doesn't
address whether the recipient needs to see actions differently from
events -- as "your state has changed" is just a subtype of "state has
changed". I believe we answer this by articulating the
requirements/constraints on action handlers vs.
requirements/constraints on event handlers. As this message is
about terminology I will leave this discussion to another message.
-Mike-
Rich Thompson wrote:
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 Böblingen , Germany
Tel.: +49-7031-16-4603, Fax: +49-7031-16-4401
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| | <yossi.tamari@sapp|
| | ortals.com> |
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| | 04/22/2002 03:31 |
| | PM |
| | Please respond to |
| | "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 Böblingen , Germany
Tel.: +49-7031-16-4603, Fax: +49-7031-16-4401
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