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An Effective Detection Method of Anomalous Sequences Considering the Occurrence Order and Time Interval of the Elements
http://doi.org/10.5626/JOK.2021.48.4.469
Recently, a rapid generation of sequence data consisting of elements in various applications has been witnessed over time. Although various methods for detecting anomalous sequences among the given sequences have been actively studied, most of them mainly consider only the occurrence order of the elements. In this paper, we propose an effective anomalous sequence detection method considering not only the occurrence order of the elements but also the time interval between the elements. Apparently, the proposed method uses a model that combines two autoencoders. The first is an LSTM autoencoder, which learns the features of the occurrence order of elements, and the second is a graph autoencoder, which learns the features of the time interval between the elements. After completion of the training, each sequence is input to the trained model and reconstructed by the trained model. If the occurrence order and time interval of elements in the reconstructed sequence greatly differ from those in the original sequence, the corresponding sequence is determined as an anomalous sequence. Through various experiments using synthetic data, we confirmed that the proposed method can detect anomalous sequences more effectively than the method that uses an RNN autoencoder to learn the occurrence order of the elements, the methods that use a single LSTM autoencoder and the method that doesn’t use deep learning model.
An Embedding Technique for Weighted Graphs using LSTM Autoencoders
http://doi.org/10.5626/JOK.2021.48.1.13
Graph embedding is the representation of graphs as vectors in a low-dimensional space. Recently, research on graph embedding using deep learning technology have been conducted. However, most research to date has focused mainly on the topology of nodes, and there are few studies on graph embedding for weighted graphs, which has an arbitrary weight on the edges between the nodes. Therefore, in this paper, we proposed a new graph embedding technique for weighted graphs. Given weighted graphs to be embedded, the proposed technique first extracts node-weight sequences that exist inside the graphs, and then encodes each node-weight sequence into a fixed-length vector using an LSTM (Long Short-Term Memory) autoencoder. Finally, for each graph, the proposed technique combines the encoding vectors of node-weight sequences extracted from the graph to generate one final embedding vector. The embedding vectors of the weighted graphs obtained by the proposed technique can be used for measuring the similarity between weighted graphs or classifying weighted graphs. Experiments on synthetic and real datasets consisting of groups of similar weighted graphs showed that the proposed technique provided more than 94% accuracy in finding similar weighted graphs.
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