The USPC system provides for the storage and retrieval of every U.S. patent document. Therefore, in the aggregate, the system must be exhaustive of all patentable subject matter under patent laws. Although the system is primarily designed to assist patent examiners performing patentability searches, the system is used by a wide variety of other users, e.g., patent attorneys and agents, people involved in research and development, and the patrons of the Patent and Trademark Depository Library (PTDL) system. The present USPC system reflects the uneven growth derived from the first general scheme created in 1900. Classification before 1900 closely paralleled economic groupings of the period with informal and arbitrary subdivisions to provide manageable size collections. Relationships among such patent collections, if they existed, were lost in the alphabetical ordering of titles assigned to each of the collections Search notes, class and subclass definitions, or schedule explanations either did not exist...