1. A method to maintain active queries, the method comprising: executing a query based on data items in at least two relations in a database, the executing including outputting a query result and control information associated with the query; recording the query result and the control information; receiving a notification that at least one of the data items has been updated subsequent to the executing; modifying the query result to reflect the data items that were updated subsequent to the executing, the modifying responsive to the control information wherein the control information includes a sensitivity index that indicates potential impacts on the query result when selected data items are updated.