[standards-jig] JEP0024, namespaces and permissions...

Timothy Carpenter timbeau_hk at yahoo.co.uk
Fri Jul 12 11:11:38 UTC 2002


As I am in the process of building a real-time information transport on
Jabber, I am interested in pub:sub.

1) Is it possible to clarify that pub:sub namespaces have to be expressed in
terms relative to the publisher, not the sender? Such items as
news:political:home asked of a France-based international news publisher by
someone from the UK would provide French domestic news!

Alternatively, advise against relative namespaces or permit namespace
translation? (I prefer the former)

2) Data may have more than one 'namespace'...in fact NEWS especially has the
possibility of tens of classifications per story - e.g. politics, drugs, US,
police, Washington, Civil Rights, election etc. The alternative is to have
embedded codings as payload data and filter after the delivery, which many
systems do already with the obvious bandwidth and processing implications on
the last mile. 

I would suggest to avoid confusion, that the news namespace be altered in
JEP0024 to suggest something that would work as a more unique namespace, if
only one namespace can be given to data by the publisher. E.g.
automobiles:mercedes:W108.

Alternative is duplicating messages with different namespaces or multiple
namespaces sent by the publisher...
"news:[politics|US|Police|Washington|drugs|heroin|crime]:wires"? The pub:sub
entity would then have to filter on this, or the client filters at the other
end.

The centralised filtering allows for lower bandwidth last mile dumb
streaming to the client device but puts a greater load on the server to sift
multiple namespace combinations. Server should have right to refuse.

With the current framework, we are only able to send multiple messages from
the publisher to achieve namespace granularity, so placing an assumption on
the architecture. If we allow "polynamespacing" then we have further choices
of filtering at server or client. This allows us to decide trade-offs of cpu
and bandwidth. 

A mobile phone streamer, for example, would prefer polynamespace filtering
at the server. The publisher may like to have polynamespace publishing (once
only per item), but intermediate caches with terrestrial, high powered
data-hungry clients would perfer to have client-side filtering by streaming
over a few multicast channels.

(It may be worth warning namespacer's to be aware of the implications of
multicast delivery on namespace allocation)

3) Permissions are not included in the spec, but from a publisher's (and
even redistributor's) point of view, it needs to send out information to
control that and in a way that sits comfortably alongside the pub:sub
framework. This is not easy, from long experience in data distribution
systems (16 yrs Reuters/Tibco).

BTW: I am looking into permissions for my real time data architecture I am
building. Central and distributed, grant and deny.

4) Finally and trivially..I would like to confirm if namespaces can be
'sticky' within a node, such that a headline, body and other information
(subject codes) have the same namespace without repeating it for each field.

If not, it would be preferable to have some form of "~:" or other operator
to say "whatever, plus...". Forgive me if this is already sorted, but it was
not clear to me (my fault) from the short data payloads of the examples in
JEP0024.

Thanks 
Tim Carpenter


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