Improving the classification accuracy of streaming data using SAX similarity features

The classification accuracy of time series is highly dependent on the quality of used features. In this study, features of new type, called SAX (Symbolic Aggregate approXimation) similarity features, are presented. SAX similarity features are a combination of the traditional statistical number-based and the template-based classification. SAX similarity features are obtained from the data of the time window by first transforming the time series into a discrete presentation using SAX. Then the similarity between this SAX presentation and predefined SAX templates are calculated, and these similarity values are considered as SAX similarity features. The functioning of these features was tested using five different activity data sets collected using wearable inertial sensors and five different classifiers. The results show that the recognition rates calculated using SAX similarity features together with traditional features are much better than those obtained employing traditional features only. In 20 tested cases out of 23, the improvement is statistically significant according to the paired t-test.

► The study presents features of new type, called SAX (Symbolic Aggregate approXimation) similarity features.
► SAX similarity features are a combination of the traditional statistical number-based and the template-based classification.
► Features are tested using five different data sets and classifiers.
► In 20 tested cases out of 23 the presented method improved classification accuracy significantly according to paired t-test.