Advances in hardware technology have led to new ways of collecting data at a more rapid rate than before. For example, many transactions of everyday life, such as using a credit card or a phone, lead to automated data collection. Similarly, new ways of collecting data, such as wearable sensors and mobile devices, have added to the deluge of dynamically available data. An important assumption in these forms of data collection is that the data continuously accumulate over time at a rapid rate. These dynamic data sets are referred to as data streams.