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Time series classification using multiple representations and ensembles

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Rafael Giusti
Total Authors: 1
Document type: Doctoral Thesis
Press: São Carlos.
Institution: Universidade de São Paulo (USP). Instituto de Ciências Matemáticas e de Computação (ICMC/SB)
Defense date:
Examining board members:
Gustavo Enrique de Almeida Prado Alves Batista; Alexandre Plastino de Carvalho; Marcos Gonçalves Quiles; Marcela Xavier Ribeiro; Agma Juci Machado Traina
Advisor: Gustavo Enrique de Almeida Prado Alves Batista

Temporal data are ubiquitous in nearly all areas of human knowledge. The research field known as machine learning has contributed to temporal data mining with algorithms for classification, clustering, anomaly or exception detection, and motif detection, among others. These algorithms oftentimes are reliant on a distance function that must be capable of expressing a similarity concept among the data. One of the most important classification models, the 1-NN, employs a distance function when comparing a time series of interest against a reference set, and assigns to the former the label of the most similar reference time series. There are, however, several domains in which the temporal data are insufficient to characterize neighbors according to the concepts associated to the classes. One possible approach to this problem is to transform the time series into a representation domain in which the meaningful attributes for the classifier are more clearly expressed. For instance, a time series may be decomposed into periodic components of different frequency and amplitude values. For several applications, those components are much more meaningful in discriminating the classes than the temporal evolution of the original observations. In this work, we employ diversity of representation and distance functions for the classification of time series. By choosing a data representation that is more suitable to express the discriminating characteristics of the domain, we are able to achieve classification that are more faithful to the target-concept. With this goal in mind, we promote a study of time series representation domains, and we evaluate how such domains can provide alternative decision spaces. Different models of the 1-NN classifier are evaluated both isolated and associated in classification ensembles in order to construct more robust classifiers. We also use distance functions and alternative representation domains in order to extract nontemporal attributes, known as distance features. Distance features reflect neighborhood concepts of the instances to the training samples, and they may be used to induce classification models which are typically not as efficient when trained with the original time series observations. We show that distance features allow for classification results compatible with the state-of-the-art. (AU)

FAPESP's process: 12/08923-8 - Times Series Classification Using Different Data Representations and Ensembles
Grantee:Rafael Giusti
Support type: Scholarships in Brazil - Doctorate