1. Introduction
The quantity of data stored in computers is growing rapidly. Much of this data, particularly data collected automatically by sensing or monitoring applications, is time-series data. A time series is a real-valued sequence, which represents the status of a single variable over time. The monitored activity can be a process defined by some human activity, like the fluctuations in Microsoft stock closing prices, or a natural process, like Lake Huron historical water levels. The presence of a time component in data is what unifies such diverse data sets and classifies them as time series. Therefore, it is hardly surprising that much research has been devoted recently to the efficient management of time-series data [1], [24], [16], [19], et al].