[standards-jig] JEP-0060 PubSub question on meta-nodes

Ralph Meijer jabber.org at ralphm.ik.nu
Sat Jan 10 18:37:52 UTC 2004


On Sat, Jan 10, 2004 at 05:55:46PM +0100, troyer wrote:
> Hello All,
> 
> I had a good look through the JEP-0060 PubSub mechanism and had a few
> questions about the semantics of a meta-node.  Section 9 of the document
> seems to only discuss a meta node as a system node used for internal
> management purposes.
> 
> Is there any notion of a hierarchy of nodes using the meta node concept?
> 
> For example, suppose that I have 4 different groups of colleagues with
> which I communicate and share presence via IM on a regular basis.  It
> would be easy enough to create a node for each group and then add each
> of the group members as subscribers to the appropriate node.  I would
> then be able to alter my published presence to different states for each
> group. 
> 
> Would it be possible to create a meta-node that "owns" each of the 4
> group nodes I created?

Yes and no.

You can make an entity that subscribes to all four nodes and republishes
the notifications it receives on another node (the meta node). Of course,
you can merge the pubsub component and this entity and have a meta node
concept in the pubsub component which is just a simple programmatic exercise.

There is no protocol (so far) to manage such special arrangements, but you
could make a special, implementation dependent, node configuration option that
keeps a list of other nodes that this node proxies. Such an implementation
should of still ask if that meta node may subscribe to the owner of the
original node.

> If so, 2 questions:
> 
> What would be the implication of publishing an item to the meta-node?
> Would the children nodes forward it to their individual list of
> subscribers?

That is the other way around. In the scenario I described above, the meta
node has no real publishers, it publishes internally by relaying received
notifications to its own subscribers. You could of course have the child
nodes allow the meta node as publisher and have the meta node relay the
publish requests it receives to the child nodes.

> If an item were published to a child node, would that imply that the
> node is published to the direct subscribers of the meta-node?

If you've done it like above, yes.

You've essentially built a two way proxying publish/subscribe system.

> Thanks for any feedback..

My head is spinning, how is yours?

-- 
Groetjes,

Ralphm



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