Selectivity estimation in temporal databases
Himawan Gunadhi, A. Segev, Jeyaveerasingam George Shanthikumar · eScholarship (California Digital Library) · 1990
Temporal relations possess several characteristics that distinguish them from conventional snapshot relations.First, for each instance of the surrogate (entity) there is a set of timeordered tuples.Second, surrogate instances may arrive and depart in some time-dependent manner.Third, the surrogate instance may arrive and depart more than once, thus creating gaps (null values) within its history.Lastly, the value of the temporal attribute may be also be time-dependent.Conventional methods of estimation are incapable of providing good approximations of the cost of various temporal operations, even for those involving selections on a single relation.The problem is more acute in the case of join operations, since selectivities on time interval intersections have to be estimated.We propose a practical, yet theoretically sound model to characterize the behavior of temporal relations.Estimates of the outcome for various unary and binary operations are derived from this model.Preliminary results on the accuracy of selected estimates are provided .