Online Incremental Structure Learning of Sum-Product Networks

Sum–product networks (SPNs) are deep architectures that can learn and infer at low computational costs. The structure of SPNs is especially important for their performance; however, structure learning for SPNs has until now been introduced only for batch-type dataset. In this study, we propose a new online incremental structure learning method for SPNs. We note that SPNs can be represented by mixtures of basis distributions. Online learning of SPNs can be formulated as an online clustering problem, in which a local assigning instance corresponds to modifying the tree-structure of the SPN incrementally. In the method, the number of hidden units and even layers are evolved dynamically on incoming data. The experimental results show that the proposed method outperforms the online version of the previous method. In addition, it achieves the performance of batch structure learning.