Discriminative Learning of Mixture of Bayesian Network Classifiers for Sequence Classification

A mixture of Bayesian Network Classifiers(BNC) has a potential to yield superior classification and generative performance to a single BNC model. We introduce novel discriminative learning methods for mixtures of BNCs. Unlike a single BNC model where the discriminative learning resorts to a gradient search, we can exploit the properties of a mixture to alleviate the complex learning task. The proposed method adds mixture components recursively via functional gradient boosting while maximizing the conditional likelihood. This method is highly efficient as it reduces to generative learning of a base BNC model on weighed data. The proposed approach is particularly suited to sequence classification problems where the kernels in the base model are usually too complex for effective gradient search. We demonstrate the improved classification performance of the proposed methods in an extensive set of evaluations on time-series sequence data, including human motion classification problems.