28. A method of querying arbitrarily structured records in a database, the method being implemented in a query engine, the query engine being executable by a processor operably connected to a memory device, and the method comprising the following steps executed in an order and repetition determined by the query engine: building, in a memory device, a query structure containing a selection criterion and information defining a query; retrieving indicia of records from the database in accordance with the query structure; evaluating each of the indicia according to the selection criterion to determine whether the indicia satisfy the selection criterion; and returning selected indicia that satisfy the selection criterion.
28. A method of querying arbitrarily structured records in a database, the method being implemented in a query engine, the query engine being executable by a processor operably connected to a memory device, and the method comprising the following steps executed in an order and repetition determined by the query engine: building, in a memory device, a query structure containing a selection criterion and information defining a query; retrieving indicia of records from the database in accordance with the query structure; evaluating each of the indicia according to the selection criterion to determine whether the indicia satisfy the selection criterion; and returning selected indicia that satisfy the selection criterion. 37. The method of claim 28, wherein the evaluating step further comprises evaluating an operator having an operand of unknown value.