ID primitive

On today's Teleconference the ID primitive was briefly discussed.  Karl
Seiler recommended that we look at what data should be encompassed in a
POI's idea. Does it encompass geodata? Other Data? Surely there is something
better than a 64bit number.

While I dont have a solution I do have a few thoughts.

With the assumption that the ID is permanent, can it include info that is
not permanent? For example if there is a POI for a Circus and we include
Geodata in the ID does that imply that circus can not move? If as discussed
a POI has a relative location how is that capture?

Is there a decent permanent piece of information that can be added to the
ID? Or is location fine except for the edge cases above?