[Tracker] Query to create an object only if it doesn't exist...

[Maia McCormick <maia mcc gmail com>]

Hey folks! Need help putting together a tracker query for GNOME Music--this question is for Martyn or anyone else who can help me out.

Basically, I want to see if a nao:Tag with rdfs:comment 'foo' exists, and if it doesn't, create it. (If it does exist, though, I want to leave it intact--same urn, same tracker id, etc.) How might I do this?

Thanks a bunch!
Maia, for GNOME Music via OPW