[cap-talk] Client Utility/E-speak Pub/Sub

[Karp, Alan H]

A subject line so most of you can delete the mail without even opening
it.

Jed wrote:
> 
> What would induce a publisher to register with a distributor?
> Perhaps I should clarify my question by asking what interest
> "publisher"s had in doing such publishing.  Given that publishing
> was happening, I can see the value of a distributor.  However,
> I don't understand the base value to the publisher to begin with.
> 
Pub/sub is used when you know you're generating interesting events, but
you don't know all the ways you might want to use them.  Rather than
upgrading the system generating the events every time you change your
mind, you publish those events and add subscribers to add functionality.
Hence, Pub/sub assumes cooperating entities.  In our case, the core
published events that eventually reached the management GUI.  Other
components published events that went to their billing systems.  
> 
> This topic came up in the context of logged events.  Why would
> a service capable of logging do so in a potentially public
> forum?  Couldn't such logs be seen more as a possible invasion
> of privacy (and thus a negative) than as a potentially useful
> service for users?

The forum wasn't public.  A publisher could assume that subscribing to
the distributor was controlled in a manner consistent with the
publisher's policy.  In practice, the publisher, distributor, and
subscribers all came from the same source.  Our first customer, a
Finnish University doing distance learning, generated an event for each
segment of a lecture delivered to a student.  This event ended up in
their billing records, which allowed them to charge only for what the
student accessed.

> > The event system itself had a novel control mechanism based on split
> > capabilities.  I can provide more detail if anyone is interested.
> 
> If it might help resolve my concern about "privacy"
> issues regarding 'who' is authorized to see logs then
> certainly I am interested.
>
Actually, the access control was more about who could send an event to
you than it was which events you could see.  Which events you could see
was controlled by which distributors you had capabilities to.  In CU,
only subscribers that came with the core were given the capability to
the distributor for core events.

________________________
Alan Karp
Principal Scientist
Virus Safe Computing Initiative
Hewlett-Packard Laboratories
1501 Page Mill Road
Palo Alto, CA 94304
(650) 857-3967, fax (650) 857-7029
https://ecardfile.com/id/Alan_Karp
http://www.hpl.hp.com/personal/Alan_Karp