National Library of Medicine (NLM) Classification Scheme
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The National Library of Medicine (NLM) classification scheme is widely-used throughout the world to organize materials in health, medical and allied health libraries. As a classification system, it covers the main areas of medicine as well as the the preclinical sciences arranging books and other physical items from QS through the WZs. The scheme is suitable for large and small collections (and even specialized collections) of materials. Patterned after the Library of Congress (LC) scheme, the NLMC uses the same principle of alphabetic letters for broad subject categories (and shelf-browsing) which are then subdivided by numbers and "cuttered" (see Charles Ammi Cutter). From the fifth edition (1994): "The National Library of Medicine Classification covers the field of medicine and related sciences, utilizing schedules of QZ and W-WZ permanently excluded from LOC."
In the 1940s, the Army Medical Library found it necessary to create a special scheme for medical books. A preliminary edition was prepared by Mary Louise Marshall in 1948, and later revised by Frank B. Rogers. The Rogers version was published in 1951 as the first edition of the Army Medical Library Classification; the second edition was published in 1958 as the National Library of Medicine (NLM) Classification; the third edition in 1964; the fourth in 1978 and a revision of the 4th in 1981. The fifth major revision came in 1994.
NLM scheme building blocks for findability
Main schedules & facets of NLM scheme
The main schedules QS-QZ, W-WY, and WZ (excluding WZ 220-270) are used to classify works published after 1913; the 19th century schedule is used for works published 1801-1913; and WZ 220-270 to provide century groupings for works published before 1801. One- or two-letter alphabetical codes use a limited range of letters: only QS-QZ and W-WZ. This allows co-existence with LC (QS-QZ and W-WZ are not used in LC). Three existing codes in LC overlap with NLM: Human Anatomy (QM), Microbiology (QR), and Medicine (R). Headings for individual schedules (letters, or letter pairs) are given in brief (ie. QW - Microbiology and Immunology; WG - Cardiovascular System), and provide an outline of the subjects covered. Headings are interpreted broadly and include physiology, specialties connected with them, regions of the body chiefly concerned and subordinate related fields. NLM is hierarchical, and are divided by organ systems. The main schedules begin with a group of form numbers from 1-49 used to classify materials by publication type, ie., dictionaries, atlases, laboratory manuals. NLM applies subject classification to materials treated as monographs. Serial publications are separated by form, and are assigned classification numbers within several broad categories. Classification numbers are assigned to works determined by the subject content of works. Those dealing with several subjects falling into different areas of the classification are classed by emphasis or where emphasis is lacking by the first subject treated. Works on particular diseases are classified with the disease, which in turn is classified with the organ or region affected, regardless of special emphasis on form of therapy or diagnostic procedure.
NLM Classification - broad facets/categories
Medicine and Related Subjects