Teoma uses something they call "Subject Specific" and "Communities" to rank their sites. Basically, a well ranked site needs to be within some type of subject specific category and part of a community. (I am still a bit foggy on the subject specific concept) But as Paul Gardi explained, everything in the world can be broken down into a community. He gave an example at the conference, people wearing blue shirts and have brown hair - that is a community. Anyway... Within those concepts is an other concept of hubs. Each community might have one hub or many hub. A hub is basically a site that links to other smaller sites, so a hub can link to an other hub or not. A site can link to a site and then link back to a hub.
The more a site is linked to within a community and (more importantly) the more authoritative a site linking to an other site is, the more weight that site is given. They are trying to figure out what the "expert sites" are and based on those experts sites, decide on what other sites for keywords within that community rank.