The Autonomy folks must be getting worried about the progress of taxonomy applications and the precision and recall that such systems provide. Autonomy and Google live on relevance rankings as the return to the user. Relevance to me is a confidence game. It is the best guess of the system as to whether the results returned will actually match the user's request. If you have a big enough data set returned, certainly something in there will be useful. But the sheer amount of items the user has to review (or amount of noise they have to look at) is very annoying. So they rank the returns by relevance based on a number of statistical factors so the most likely items based on co-occurrence with terms matches and near matches will appear at the top of the list - that is, they will be relevance ranked.