National Library of Medicine (NLM) Classification Scheme

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Introduction

See also Classification & indexing in health libraries and Medical Subject Headings (MeSH)

The U.S. National Library of Medicine classification (NLMC) is a classification scheme covering the main areas of medicine as well as the preclinical sciences. NLMC is suitable for use in both large and small collections as well as specialized collections.

Patterned after the Library of Congress classification (LC) system, the NLM scheme uses alphabetical letters denoting broad subject categories which are subdivided by numbers. In the NLM scheme QW 279 indicates a book on one aspect of microbiology. Both NLM and LC are noted for their alphabetical letters denoting broad categories, further subdivided by numbers in increasing levels of specificity. 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 early 1940s, the U.S. Army Medical Library (now NLM) found it necessary to create a specialized scheme for medical books. A preliminary edition was prepared by Mary Louise Marshall in 1948, which was later revised by Dr. Frank B. Rogers in 1950. 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.

Revisions 2012

• NLM Classification Update 2012 <http://www.nlm.nih.gov/class/> has been revised as follows:

• 37 class numbers added
• 178 class number captions or notes modified
• 4 class numbers canceled
• 2 Table G numbers (Geographic notation) added for South Korea (JK6) and North Korea (JK7); Korea was moved to the Historical Geographic Locations section retaining the same Table G (JK6)
• 88 index main headings added
• 578 index entries modified
• 218 index headings deleted

NLM scheme building blocks for findability

Used by medical and health science libraries at colleges and universities the world over, the NLM scheme is one of the few specific medical classification systems ever developed. The one- and two-letter alphabetical codes employ a limited range of letters, only QS-QZ and W-WZ. This allows the system to co-exist with LC (QS-QZ and W-WZ are not used in LC). The three pre-existing codes in the LC system overlap with NLMC: Human Anatomy (QM), Microbiology (QR), and Medicine (R). Headings for individual schedules (letters or letter pairs) are given in brief form (e.g., QW - Microbiology and Immunology; WG - Cardiovascular System) and together provide an outline of the subjects covered by NLM. Headings are interpreted broadly and include physiology and specialties connected with them, regions of the body chiefly concerned and subordinate related fields. NLMC is hierarchical, and within each schedule, division by organ usually has priority. Each schedule, and sections within, begins with a group of form numbers ranging from 1-49 which are used to classify materials by publication type, e.g., dictionaries, atlases, lab manuals, etc.

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

References

• Coyle K, Hillmann D. Resource description and access (RDA). D-Lib Magazine. 2007;13(1/2):1082.
• Giustini D. Tracing the organizing tools of health library collections. The Search Principle blog. 17 August 2008
• Harper CA, Tillett BB. Library of congress controlled vocabularies and their application to the semantic web. Cataloging & Classification Quarterly. 2007; 43(3-4).
• Lopez-Mertz EM. The adequacy of the structure of the National Library of Medicine classification. Library Resources & Technical Services. 1997;41(2):123-135.
• Lyndenberg HM. John Shaw Billings: creator of the National Medical Library, and its catalogue. Chicago: American Library Association, 1924.
• MacCall SL. Online medical books: their availability and an assessment of how health sciences libraries provide access on their public websites. JMLA. 2006;94(1):75–80.
• National Library of Medicine. Fact Sheet NLM Classification.
• Womack KR. Conformity for conformity's sake? The choice of a classification system and a subject heading system in academic health sciences libraries. Cataloging & Classification Quarterly. 2006;42(1).