1. The 20 newsgroups data set, http://www.ai.mit.edu/jrennie/20Newsgroups/
2. dmoz - open directory project, http://dmoz.org/
3. Internet movie database, http://www.imdb.com
4. Baeza-Yates, R., Ribeiro-Neto, B.: Modern Information Retrieval. Addison-Wesley, Reading (1999)
5. Breiman, L.: Bagging predictors. Machine Learning 24(2), 123–140 (1996)