According to an example implementation, at least one non-transitory computer-readable storage medium may include instructions stored thereon. When executed by at least one processor, the instructions may be configured to cause a computing system to select at least one function type to approximate an interval of data points within a time series, the at least one function type being less than all of a plurality of functions available to approximate the interval, while the first function type will approximate the interval of data points within a maximum allowable error, add data points from the time series to the interval, and when the first function type will no longer approximate the interval with the added data points within the maximum allowable error, select a function of a different type or a function of a different term from the plurality of functions to approximate the interval with the added data points.