1. An apparatus for querying a database comprising records, the apparatus comprising a digital computer having a processor operably connected to a memory device storing modules executable on the processor and data structures containing data associated with the modules, the modules and data structures comprising: arbitrarily structured records stored in the memory device; a query structure stored in the memory device and representing a selection criterion; and a query engine module stored in the memory device to be executable by the processor to build the query structure and to retrieve indicia of records satisfying the query.
1. An apparatus for querying a database comprising records, the apparatus comprising a digital computer having a processor operably connected to a memory device storing modules executable on the processor and data structures containing data associated with the modules, the modules and data structures comprising: arbitrarily structured records stored in the memory device; a query structure stored in the memory device and representing a selection criterion; and a query engine module stored in the memory device to be executable by the processor to build the query structure and to retrieve indicia of records satisfying the query. 12. The apparatus of claim 1, wherein the query engine is programmed to evaluate an operator having a multi-valued operand, having one or more values corresponding thereto and arising from a single record.