Weka is a collection of machine learning algorithms for data mining tasks. The algorithms can either be applied directly to a dataset or called from your own Java code. Weka contains tools for data pre-processing, classification, regression, clustering, association rules, and visualization. It is also well-suited for developing new machine learning schemes.

Look at the Bayesian Network Classifiers, FAQ at:

http://www.cs.waikato.ac.nz/~remco/weka_bn/node24.html

There is also a bigger comprehensive documentation at:

http://www.cs.waikato.ac.nz/~remco/weka_bn/index.html

Source: Weka FAQ