Given two sets S1, S2 of moving objects, a future timestamp tq, and a distance threshold d, a
spatio-temporal join retrieves all pairs of objects that are within distance d at tq. The
selectivity of a join equals the number of retrieved pairs divided by the cardinality of the
Cartesian product S1× S2. This paper develops a model for spatio-temporal join selectivity
estimation based on rigorous probabilistic analysis, and reveals the factors that affect the
selectivity. Initially, we solve the problem for 1D (point and rectangle) objects whose location …