12. The probabilistic clustering system as set forth in claim 8 , wherein the classes are organized into a hierarchy of classes with documents assigned to leaf classes of the hierarchy, the user interface is configured to receive a user selection to split a pre-existing leaf class into two or more split leaf classes, and the processor is configured to (i) perform clustering training to associate each document of the pre-existing leaf class with one of the two or more split leaf classes, the cluster training being limited to documents associated with the pre-existing leaf class and generating local probabilistic model parameters for characterizing the split leaf classes respective to the documents associated with the pre-existing leaf class and (ii) algebraically combine the local probabilistic model parameters of each split leaf class and the probabilistic parameters of the pre-existing leaf class to produce probabilistic model parameters characterizing the two or more split leaf classes respective to the documents of the probabilistic clustering system.
12. The probabilistic clustering system as set forth in claim 8 , wherein the classes are organized into a hierarchy of classes with documents assigned to leaf classes of the hierarchy, the user interface is configured to receive a user selection to split a pre-existing leaf class into two or more split leaf classes, and the processor is configured to (i) perform clustering training to associate each document of the pre-existing leaf class with one of the two or more split leaf classes, the cluster training being limited to documents associated with the pre-existing leaf class and generating local probabilistic model parameters for characterizing the split leaf classes respective to the documents associated with the pre-existing leaf class and (ii) algebraically combine the local probabilistic model parameters of each split leaf class and the probabilistic parameters of the pre-existing leaf class to produce probabilistic model parameters characterizing the two or more split leaf classes respective to the documents of the probabilistic clustering system. 13. The probabilistic clustering system as set forth in claim 12 , wherein the two or more split leaf classes one of (i) replace the pre-existing leaf class, and (ii) are arranged as immediate descendant classes of the pre-existing leaf class, the documents being removed from the pre-existing leaf class and associated with the two or more split leaf classes by the cluster training.