I'm here at the InfoVis conference in Sacramento and a conversation with Marti Hearst over at UCBerkeley just reminded me why I have been bothered by the 'confusion' between the phrases "social tagging" and "collaborative tagging" for quite some time. In fact, Wikipedia has a redirection of "Social Tagging" to "Collaborative Tagging" (see http://en.wikipedia.org/w/index.php?title=Social_tagging&redirect=no). This, I would argue, is wrong. Why?
'Collaborate', according to the American Heritage Dictionary, is "to work together, especially in a joint intellectual effort." The problem is that tagging features in many of the popular Web2.0 tools such as Flickr and YouTube are not really 'collaborative', since users aren't really working together per se. In YouTube, for example, only the uploader of the original video clip can specify and edit the tags for an video. Most of the time, in Flickr, one only tag their own photos. However, Flickr is somewhat more collaborative than YouTube because the default setting for any account is to allow contacts such as friends and families to also tag the photos.
Both of these two systems don't seem that 'collaborative', because, to me, collaboration implies shared artifact, shared workspace, and shared work. On the other hand, 'social' is "living or disposed to live in companionship with others or in a community, rather than in isolation". In other words, simply existing and having some relation to others in a community. So for example, I would argue that in YouTube, we have social tagging but not collaborative tagging, because while users tag their uploaded videos in the context of a online social community, and they do not collaborate to converge on a set of tags appropriate for that video.
The use of the term 'collaborative' in past Computer-Supported Cooperative Work (CSCW) field has especially come to imply
a shared workspace. With shared workspaces, often there are some elements of coordination and conflicts involved as well (and hopefully conflict resolution as well). So in contrast to YouTube, the most 'collaborative' tagging system I know is the category tagging system in Wikipedia. Anyone can edit the category tags for an article. They can remove, add, discuss, and revert the use of any tag. In this case, the category tags are shared artifacts that anyone can edit inside a shared workspace. The work of tagging all 2 Million+ articles in Wikipedia is shared work among the community.
It's perhaps interesting to note that somewhere in between YouTube and Wikipedia tagging is perhaps the bookmarking system del.icio.us. In del.icio.us, there is a shared artifact (the tagged sites or URLs), and there is shared work of tagging all of the websites and pages out there on the Web. However, there is less of a notion of a shared workspace. My tags for an URL could be and probably is different from someone else's tags for the same URL. I also have the capability of searching within just my own del.icio.us space. So from least collaborative to the most collaborative, we have YouTube, then del.icio.us, and then finally the category tagging system in Wikipedia.
A simple way to explain this is that one must be social in order to collaborate, but one need not be collaborative to be social. So in summary, I would argue that social tagging is a superset of collaborative tagging. But a social tagging system may not necessarily be a collaborative tagging system. We should change the definitions in Wikipedia to distinguish between these two types of systems.