[Standards-JIG] pubsub: transient+notification

Peter Saint-Andre stpeter at jabber.org
Sat Feb 18 04:02:09 UTC 2006


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Ralph Meijer wrote:
> On Tue, Feb 14, 2006 at 02:32:27PM -0700, Peter Saint-Andre wrote:
>> JEP-0060 lists as one of the possible node types "transient +
>> notification" -- i.e., the node sends out no payloads but instead sends
>> out only notification with no ItemIDs. The use case for this is quite
>> unclear to me, since subscribers would get things like this:
>>
>> <message from='pubsub.shakespeare.lit' to='francisco at denmark.lit'>
>>   <event xmlns='http://jabber.org/protocol/pubsub#event'/>
>> </message>
>>
>> To me, that's the equivalent of telling the subscriber "hey, something
>> happened, but I can't tell you what it is nor can I give you a way to
>> find out what it is, since there's no payload or item associated with
>> this event". Which strikes me as pretty useless.
> 
> This is really the most basic publish/subscribe use case. The usage of
> data in the notifications or having persistence are enhancements on the
> basic concept.
> 
> What you say here is that a subscriber wants to be notified when some
> event has taken place. What kind of event, its meaning really, is
> application specific. Example:
> 
> One could imagine a node representing that your doorbell button has
> been pushed. It doesn't matter for how long, or when the doorbell
> button was unpushed, so no data is required. Also, you don't want to
> have a history of doorbell pushes, so no persistence is required. You
> only want to be notified if and when the doorbell button has been
> pushed.

Ah, that's a good example. :-)

> The confusion may arise from your flawed example event, because it
> must always have a <items/> element when notifying a publish:
> 
> 
>   <message from='pubsub.shakespeare.lit' to='francisco at denmark.lit'>
>     <event xmlns='http://jabber.org/protocol/pubsub#event'>
>       <items node='generic/doorbell'/>
>     </event>
>   </message>
> 
> By the way, for removing items (in the persistent node case), I noticed
> that the <retract/> child of <items/> is not mentioned in the schema.

Fixed.

Peter

- --
Peter Saint-Andre
Jabber Software Foundation
http://www.jabber.org/people/stpeter.shtml

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