S Sliding-Window Aggregation Algorithms

An aggregation is a function from a collection of data items to an aggregate value. In slidingwindow aggregation, the input collection consists of a window over the most recent data items in a stream. Here, a stream is a potentially infinite sequence of data items, and the decision on which data items are most recent at any point in time is given by a window policy. A sliding-window aggregation algorithm updates the aggregate value, often using incremental-computation techniques, as the window contents change over time, as illustrated in Fig. 1. ... ...