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Subject: Re: [wsrp] Spec defined events


I can see the argument, but such coupling with registration weakens the 
proposal, IMO.

I suppose, another assumption is that the Producer will keep track (in 
memory or persistently) of notifications sent to each Consumer making 
sure that the Consumer receives each event only once.

I still consider using an external means more elegant and useful. My 
main concern is that Consumer will have to do some amount of processing, 
however minimal it may be, at request time to consume/process these 
events, even when does not want to process all/some of such events.

Subbu

Rich Thompson wrote:
> 
>  From a protocol point of view, the known Consumers are those that have 
> registered. Non-registered Consumers are effectively sharing a guest 
> account and should not expect the Producer to track them for such 
> notifications. Producers can also have other means of tracking their 
> Consumers, but an implementation style that simply sends such events 
> because it is not known if the current Consumer has been informed should 
> be discouraged.
> 
> Rich
> 
> 
> *Subbu Allamaraju <subbu@bea.com>*
> 
> 03/14/05 11:20 AM
> 
> 	
> To
> 	wsrp@lists.oasis-open.org
> cc
> 	
> Subject
> 	Re: [wsrp] Spec defined events
> 
> 
> 	
> 
> 
> 
> 
> 
> My point is that the Producer does not always know what "each consumer"
> means.
> 
> Subbu
> 
> Rich Thompson wrote:
>  >
>  > Interesting questions. Other than the last one, they all seem predicated
>  > on an implementation style that tracks changes and does a computation
>  > upon interaction to determine whether or not to generate one of these
>  > events. Another implementation choice (that happens to avoid the bulk of
>  > these issues) is to persistently store the need to provide one of these
>  > notifications to each known Consumer and then delete the record saying
>  > the need exists when it is delivered. In addition to removing datetime
>  > computation while processing a request, this also permits notification
>  > by means other than event delivery. An example of this would be to
>  > consider a getServiceDescription invocation as removing any
>  > Producer/Portlet metadata change notifications as the response will
>  > already update the Consumer.
>  >
>  > The other point about these event definitions is that their purpose
>  > would not be to require any particular functionality, but rather to
>  > provide a standardized means by which a Producer could proactively
>  > inform a Consumer about changes. Whether or not a particular Producer or
>  > Consumer implementation makes use of this means to reduce polling for
>  > metadata would still be entirely implementation dependent.
>  >
>  > On the last question, I do not think it is up to the spec to define what
>  > a change is that should trigger any of these notifications. Rather they
>  > are defined as a means for carrying a notification that a particular
>  > form of metadata has changed. As a result of this, I would resist
>  > optimizations such as having the ProducerMetadataChanged event payload
>  > carry the new ServiceDescription. Instead, the event is just a
>  > notification and it is up to the Consumer to decide when and how to
>  > respond to the information.
>  >
>  > Rich
>  >
>  >
>  > *Subbu Allamaraju <subbu@bea.com>*
>  >
>  > 03/10/05 10:57 AM
>  >
>  >                  
>  > To
>  >                  wsrp@lists.oasis-open.org
>  > cc
>  >                  
>  > Subject
>  >                  Re: [wsrp] Spec defined events
>  >
>  >
>  >                  
>  >
>  >
>  >
>  >
>  >
>  >  > As to other options to carry such notifications by other means, why
>  >  > would we add such dependencies when we already have a channel that 
> could
>  >  > easily carry the information. I agree that the Consumer is not 
> likely to
>  >  > display the fact that it received such an event to normal 
> end-users, but
>  >  > it certainly would be valuable info to display to system admins (or
>  >  > queue for display to them).
>  >
>  > Thanks Rich. You make some good arguments. So, let me counter with few
>  > more questions.
>  >
>  > o Producers don't necessarily know whether the Consumer's version of the
>  > Producer's metadata is current or not, unless it starts to keep track of
>  > all metadata requests.
>  >
>  > o The Producer has to keep track of metadata changes persistently and
>  > make sure to cleanup those changes periodically.
>  >
>  > o The only time a Producer could return events is via handldEvent(s) and
>  > pbia responses (excluding fault conditions). This may be acceptable.
>  >
>  > o Assuming that the Producer recognized a change, how would it know
>  > whether a given Consumer should be notified or not? Should it start
>  > sending notifications to all Consumers (including those that already
>  > have the current metadata)? Such Consumers will have to do some extra
>  > processing before ignoring the event.
>  >
>  > o Should the Producer keep sending events for ever or just once? It
>  > can't be the latter since the Producer does not always know about
>  > Consumers. So, it does not know which Consumer was already notified.
>  >
>  > I think, a more fundamental question how would the spec define what a
>  > "change" is.
>  >
>  > Regards,
>  >
>  > Subbu
>  >
>  >
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