This module implements the classic "Naive Bayes" machine learning algorithm. It is a well-studied probabilistic algorithm often used in automatic text categorization. Compared to other algorithms (kNN, SVM, Decision Trees), it's pretty fast and reasonably competitive in the quality of its results. A paper by Fabrizio Sebastiani provides a really good introduction to text categorization: http://faure.iei.pi.cnr.it/~fabrizio/Publications/ACMCS02.pdf