Version:           0.10.0 (using KDE 4.2.2)
OS:                Linux
Installed from:    Ubuntu Packages

When I first defined my tag hierarchy, I started thinking about that old
guide for writing newspaper articles: the first paragraph should tell you
"who", "what", "when", "where" and "how" and the rest of the article should
elaborate.

I translated this into a tag hierarchy with "People", "Things" (e.g., still
life objects, plants, animals, etc.), "Events" (birthdays, weddings, etc.,
as dates are in Exif already), and "Places". I haven't done much about the
"how", as that is probably just Exif shooting data.

I reported a wish in bug #192442 to associate GPS co-ordinates with my
"Places" tags. This new wish is a more general case. What if tags could
be assigned a "meaning"? What if tags could be understood to represent
"People", "Things", "Places" and "Events"?

"People" tags could be associated with e-mail addresses or contact lists
and could allow integration with e-mail applications. I could e-mail all
pictures of "People/Friends/Bob" to Bob. Another bug #111600 suggested
something similar to link tags to address books.

"Things" could have links to Wikipedia. All my "Things/Flora/Oak Trees"
could link to an article about oak trees.

"Places" could have GPS co-ordinates (see bug #192442 for details).

"Events" could be associated with people (e.g., to e-mail all pictures
from a birthday party to the birthday boy/girl), or could be associated
with web sites (e.g., keep all images for an "Event" in sync with a
Flickr album so that as I edit images the album is updated). It could
also be used to reflect that photos across two or more days are closely
related, so if I take photos at a party before and after midnight,
then when I select images in the calendar, the images for the next day
will also be shown. Events might also appear in my PIM calendar as
appointments with attached photographs (after the fact).

This suggests that the semantics are not limited to one type of meaning
per tag. All tags can have associated e-mail addresses, links, online
albums, etc. in any combination that makes sense.

Star ratings could be recognised as having a meaning. You could, for
example, have all 4- and 5-star photos uploaded to an online album
automatically. Perhaps combining these with the "Events" or "Things"
tags to select the appropriate online album.

Allow tags to have a meaning and then tagging opens up all sorts of
possibilities.