Extreme multi-label text classification (XMTC) is a task for tagging each given text with the most relevant multiple labels from an extremely large-scale label set. This task can be found in many applications, such as product categorization,web page tagging, news annotation and so on. Many methods have been proposed so far for solving XMTC, while most of the existing methods use traditional bag-of-words (BOW) representation, ignoring word context as well as deep semantic information. XML-CNN, a state-of-the-art deep learning-based method, uses convolutional neural network (CNN) with dynamic pooling to process the text, going beyond the BOW-based appraoches but failing to capture 1) the long-distance dependency among words and 2) different levels of importance of a word for each label. We propose a new deep learning-based method, AttentionXML, which uses bidirectional long short-term memory (LSTM) and a multi-label attention mechanism for solving the above 1st and 2nd problems, respectively. We empirically compared AttentionXML with other six state-of-the-art methods over five benchmark datasets. AttentionXML outperformed all competing methods under all experimental settings except only a couple of cases. In addition, a consensus ensemble of AttentionXML with the second best method, Parabel, could further improve the performance over all five benchmark datasets.
Recently, to reduce the complexity, PD-Sparse @cite_8 and PPDSparse @cite_15 are proposed by the idea of sparse learning. PD-Sparse trains a classifier for each label by a margin-maximizing loss funcion with the @math penalty to obtain an extremely sparse solution both in primal and dual, without sacrificing the expressive power of the predictor. It proposes a Fully-Corrective Block-Coordinate Frank-Wolfe (FC-BCFW) algorithm to achieve a complexity sublinear to the number of primal and dual variables, and a bi-stochastic search method to improve the efficiency. PPDSparse @cite_15 is an extension of PD-Sparse, by efficient parallelization of large-scale distributed computing (e.g. 100 cores), keeping a similar performance to PD-Sparse.
@cite_15 @cite_8
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Extreme Classification comprises multi-class or multi-label prediction where there is a large number of classes, and is increasingly relevant to many real-world applications such as text and image tagging. In this setting, standard classification methods, with complexity linear in the number of classes, become intractable, while enforcing structural constraints among classes (such as low-rank or tree-structure) to reduce complexity often sacrifices accuracy for efficiency. The recent PD-Sparse method addresses this via an algorithm that is sub-linear in the number of variables, by exploiting primal-dual sparsity inherent in a specific loss function, namely the max-margin loss. In this work, we extend PD-Sparse to be efficiently parallelized in large-scale distributed settings. By introducing separable loss functions, we can scale out the training, with network communication and space efficiency comparable to those in one-versus-all approaches while maintaining an overall complexity sub-linear in the number of classes. On several large-scale benchmarks our proposed method achieves accuracy competitive to the state-of-the-art while reducing the training time from days to tens of minutes compared with existing parallel or sparse methods on a cluster of 100 cores. We consider Multiclass and Multilabel classification with extremely large number of classes, of which only few are labeled to each instance. In such setting, standard methods that have training, prediction cost linear to the number of classes become intractable. State-of-the-art methods thus aim to reduce the complexity by exploiting correlation between labels under assumption that the similarity between labels can be captured by structures such as low-rank matrix or balanced tree. However, as the diversity of labels increases in the feature space, structural assumption can be easily violated, which leads to degrade in the testing performance. In this work, we show that a margin-maximizing loss with l1 penalty, in case of Extreme Classification, yields extremely sparse solution both in primal and in dual without sacrificing the expressive power of predictor. We thus propose a Fully-Corrective Block-Coordinate Frank-Wolfe (FC-BCFW) algorithm that exploits both primal and dual sparsity to achieve a complexity sublinear to the number of primal and dual variables. A bi-stochastic search method is proposed to further improve the efficiency. In our experiments on both Multiclass and Multilabel problems, the proposed method achieves significant higher accuracy than existing approaches of Extreme Classification with very competitive training and prediction time.