1. A database server implemented method to rank non-deterministic data stored in a database implemented by a database server, the method comprising: storing a set of data tuples representing a plurality of possible instantiations of the non-deterministic data in database memory; and determining a ranking of the non-deterministic data for output by the database server in response to a query requesting a first predetermined number of data tuples collectively exhibiting a highest ranking among the set of data tuples, the determined ranking resulting in a first ranked subset of data tuples characterized in that the first ranked subset exhibits all of an exactness property, a containment property, a unique ranking property, a value invariance property and a stability property.