In the era of big data, both the size and the number of features, samples and classes continue to increase, resulting in high-dimensional classification tasks. One characteristic, among others, of big data is there exist complex structures between different classes. Hierarchical structure may be treated as the most representative one, which is mathematically depicted as a tree-like structure or directed acyclic graph. In this paper, considering data in the real world may arrive dynamically, we propose an incremental feature selection approach in hierarchical classification by employing fuzzy rough set technique. Firstly, we use the sibling strategy to reduce the scope of negative samples. Secondly, we present a theoretical analysis of the incremental updating of the lower approximation, positive region and depen-dency degree at the arrival of new samples, respectively. Thirdly, we perform the algorithmic design of the incremental approaches. To do that, we firstly present two improved versions (NIDC and NIFS for short) of the existing non-incremental methods, based on NIDC, NIFS and the aforementioned theoretical analysis, two incremental algorithms (IDU and IFS for short) are then designed to perform incremental feature selection. Lastly, a numerical experiment is conducted on some commonly used datasets for hierarchical classification tasks, whose true classes are distributed to both leaf nodes and internal nodes. A comparative study is further performed to show that our approach is effective and feasible.

Support vector machines (SVMs) are designed to solve the binary classification problems at the beginning, but in the real world, there are a lot of multiclassification cases. The multiclassification methods based on SVM are mainly divided into the direct methods and the indirect methods, in which the indirect methods, which consist of multiple binary classifiers integrated in accordance with certain rules to form the multiclassification model, are the most commonly used multiclassification methods at present. In this paper, an improved multiclassification algorithm based on the balanced binary decision tree is proposed, which is called the IBDT-SVM algorithm. In this algorithm, it considers not only the influence of “between-classes distance” and “class variance” in traditional measures of between-classes separability but also takes “between-classes variance” into consideration and proposes a new improved “between-classes separability measure.” Based on the new “between-classes separability measure,” it finds out the two classes with the largest between-classes separability measure and uses them as the positive and negative samples to train and learn the classifier. After that, according to the principle of the class-grouping-by-majority, the remaining classes are close to these two classes and merged into the positive samples and the negative samples to train SVM classifier again. For the samples with uneven distribution or sparse distribution, this method can avoid the error caused by the shortest canter distance classification method and overcome the “error accumulation” problem existing in traditional binary decision tree to the greatest extent so as to obtain a better classifier. According to the above algorithm, each layer node of the decision tree is traversed until the output classification result is a single-class label. The experimental results show that the IBDT-SVM algorithm proposed in this paper can achieve better classification accuracy and effectiveness for multiple classification problems.