[ticker-dev] Multiple presence clients for a single us er

[Phillips, Matthew]

This has been worrying me, because I couldn't find anything wrong with
David's points here, and yet I still felt there was a problem with this
approach. 

Essentially David's proposal is that clients accept the most recent status
as correct, and when you're running multiple clients they update their
internal status setting to the last info they saw go by with your name on
it.  Also, when no activity has been seen from someone for a while, all
other clients downgrade their certainty about their status (eg 'Online?').
Note that this scheme would require some sort of regular 'heartbeat' from
clients that actually know you are active (eg via keystroke monitoring) to
convince everyone else you're still there: not too pretty, but doable.

But then it dawned on me that we are forgetting that there is a lot more to
presence than status.  When I move clients my presence info may change in a
number of ways eg my 'x-Location' might change from 'Work' to 'Home' or I
might subscribe to different groups.  But in order for the most recent info
to deliver this information, clients would have to generate full info
notifications all the time, rather than the nicely efficient differential
approach currently specified.  I suppose clients _could_ set a flag when
their status is set by another client for the same person and generate a
full info next time the user changed status on that client, but I imagine
that by now we have added at least as much overhead as just maintaining more
than one presence info and displaying the 'most online' one.

My 200c worth,

Matthew.