A set of data can be obtained from different hierarchical levels in diverse domains, such as multi-levels of genome data in omics, domestic/global indicators in finance, ancestors/descendants in phylogenetics, genealogy, and sociology. Such layered structures are often represented as a hierarchical network. If a set of different data is arranged in such a way, then one can naturally devise a network-based learning algorithm so that information in one layer can be propagated to other layers through interlayer connections. Incorporating individual networks in layers can be considered as an integration in a serial/vertical manner in contrast with parallel integration for multiple independent networks. The hierarchical integration induces several problems on computational complexity, sparseness, and scalability because of a huge-sized matrix.
In this dissertation, we propose semi-supervised framework of classification and regression for a hierarchically structured network. The proposed frameworks consists of naive and approximate versions, where trade-off between performance and time complexity exists. Furthermore, we show empirical performances of hierarchical network on various task along with some real-world applications including historical faction identification, disease co-occurrence prediction, and key gene identification for Dementia.
