Flickr seems to have figured out a nice, user friendly way to use tags that have relevance to the Semantic Web. Really great idea. From the article: Like tags, there are no rules for machine tags beyond the syntax to specify the parts of a machine tag. For example, you could tag a photo with : * flickr:user=straup * flora:tree=coniferous * medium:paint=oil * geo:cartier="plateau mont royal" * geo:neighbourhood=geo:cartier http://www.flickr.com/groups/api/discuss/72157594497877875/