According to examples, an apparatus may include a processor and a memory on which is stored machine readable instructions executable by the processor to: access network traffic data pertaining to data flows among nodes in a network; partition the network traffic data into a plurality of windows; for each of the plurality of windows, aggregate data flows between pairs of nodes; compute a data distribution of each of the aggregated data flows; select a summary structure for each of the aggregated data flows based on the computed data distributions of the aggregated data flows; generate a summary of each of the aggregated data flows using the selected summary structures for the aggregated data flows; and store the generated summaries.