Social Tagging
Social tagging is a bottom-up approach to cataloging information. Traditional cataloging of information is done by experts using taxonomies or ontologies in a top-down fashion. Social tagging, on the other hand, is done by common people. People are free to choose any set of keywords that they see fit to describe a specific information.
Social tagging is a quite recent phenomenon and has being very successful for organizing information. They are used for organizing e-mail (e.g. Gmail), bookmarks (e.g. Del.icio.us), photos (e.g. Flickr), music (e.g. LastFM), video (e.g. YouTube), blog entries (e.g. WordPress), and reference entries (e.g. Wikipedia). Social tagging main advantages are a) the easiness of use, since tags correspond to a flat namespace; and b) the emergent collective intelligence, since the "selfish" effort of individuals generally helps the community as a whole.
