An order-dependent query is one whose result (interpreted as a multiset) changes if the order of the input records is changed. In a stock-quotes database, for instance, retrieving all quotes concerning a given stock for a given day does not depend on order, because the collection of quotes does not depend on order. By contrast, finding a stock's fiveprice moving-average in a trades table gives a result that depends on the order of the table. Query languages based on the relational data model...