the description is a bit vague, but iamge that you happen to like expo
you might want to retrieve the ticketoffice html page every time you
visit the expo, but if you would choose to copy it localy, then that's
your choise. nobody copies the whole of expo to their own site and
just the same with images (or icons): you shouldn't copy them, but
use them by refering to the URL.
indeed URN would be a good idea and solve the problem completely. there is
no need to define standard URN. if the URN is the same as you store locally;
then there is no need to resolve the URN or search the standard set; just
use the local copy on your disk.
this way you can still store whatever icons/text/images you want.
the problem is in another thread, about how to expire a local document.
But for icons that might not be a big problem. If the icon appear bogus at
some point; simply clear your local copies; and they will reload.
- frans