19. A computer readable storage medium having a tangible component for implementing a database having stored thereon computer readable instructions, said instructions comprising instructions for: allowing a user to request a view of data from said database, and a completeness level, the completeness level indicating a sampling of data from the view, as selected by the user, that is to be used in collecting the view statistic; collecting a view statistic regarding said view responsive to the request and the completeness level; developing at least one candidate plan for execution of a query; for at least one of said at least one candidate plan, using said view statistic to estimate the cost of said candidate plan; identifying an accuracy reading for the estimate, said accuracy reading reflecting the amount of data from which the view statistic was derived; and selecting based upon the estimate of the cost and the accuracy reading at least one of said at least one candidate plans as a recommended execution plan, wherein said step of using the view statistic to estimate the cost of said candidate plan comprises using at least one transformation rule to transform a first expression comprising all or part of said candidate plan and having an associated first expression estimate quality indicator into an equivalent second expression having an associated second expression estimate quality indicator, where said second expression comprises a reference to one or more views matching the first expression, and wherein said second expression and said first expression have an equivalent cardinality; and wherein the step of selecting the recommended execution plan comprises one of the first expression and the second expression having the higher of the first expression estimate quality indicator and the second expression estimate quality indicator.
21. The computer readable storage medium of claim 19 , where said collecting a view statistic regarding said view comprises: detecting a user request to store said view statistic; and collecting said view statistic.