Various embodiments of the present invention are directed to a method, in a computer system, for a hardware/software interface system to manipulate a plurality of discrete units of information having properties understandable by said hardware/software interface system ("Items"), said method comprising the use of a core schema to define a set of core Items which said hardware/software interface system understands and can directly process in a predetermined and predictable way. The core Items are derived from the base Item type. In certain embodiments, the Items types in the core schema cannot be directly subtyped but may instead be extended to incorporate additional properties in specific contexts without becoming inconsistent in other contexts that only comprehend the core Item type.