Despite the restricted form, there is still a wide choice of
views to materialize. The selection of views to materialize
must take into account workload characteristics, the costs for
incremental update, and upper bounds on storage
requirements. Under simplifying assumptions, a greedy
algorithm was shown to have good performance13. A related
problem that underlies optimization as well as choice of
materialized views is that of estimating the effect of
aggregation on the cardinality of the relations.