13. The system of claim 11, wherein the means for obtaining the cardinality of each component join comprise: means for retrieving a pre-computed value as the cardinality of one of the component joins.
11. The system of claim 9, further comprising: means for selecting a join order from among the possible join orders; means for obtaining an estimate of the cardinality of each component join in the selected join order; and means for calculating a value for Sigma by summing each of the cardinality estimates.