About the Classification

New Publication Pattern and Format

Scope of Revision

Classification Schedules' Structure and Development

Relationship to MeSH®

Index

New Publication Pattern and Format

Beginning with the 2002 edition, the National Library of Medicine Classification is published in electronic form and updated annually.

The online environment offers many advantages to users including hyperlinks between class numbers in the index and the schedules, and between terms within the index and direct links from these to the MeSH record itself under the MeSH Browser.

The online data creation and maintenance system of the Classification gives NLM the ability to update the classification annually in tandem with MeSH. Publication of printed editions ceased with the 5th revised edition, 1999.

Scope of Revision

This edition incorporates all 2004 additions and changes to the schedules (see Class Numbers Added and Canceled) and to the index, which has been newly edited and updated with appropriate MeSH concepts. New class numbers were added as needed to reflect changes in the biomedical and related sciences, in MeSH and the literature cataloged. Beginning with this edition, canceled class numbers appear in normal sequence within the current schedules for informational purposes. These canceled numbers are in square brackets, clearly marked with the caption: "This number not used" ( see Canceled Class Numbers).

Although the broad nature of the NLM Classification schedules precludes complete correspondence with MeSH, some class number captions were revised to reflect certain recent changes in MeSH structure and vocabulary. For example:

1. At QW 154, the caption "Spiral and curved bacteria" was replaced with "Campylobacter. Helicobacter. Spirillaceae" to better reflect current usage.
2. The class number WK 187, "Synthetic hormones," was deleted because this distinction is no longer recognized in MeSH.
3. At WB 925, the MeSH "Phytotherapy" has been added to the caption "Herbal medicine," which is now a specialty heading.
4. The caption at WV 274 has been updated from "Hearing aids" to "Hearing devices. Cochlear implants. Cochlear implantation."

In addition, a number of notes were added to various index and schedule records clarifying NLM classification practice. For example:

1. Index references to various terms for nutritional requirements and nutrition disorders in infants, children, and adolescents, were reviewed and adjusted for consistency.
2. Notes were added to clarify that works on traditional medicine, as currently practiced, are classified in WB, and works on historical practice are classified in WZ.
3. Index entries were edited to clarify that collective biography of physicians and persons in related fields from special groups are classified in WZ 150, while non- biographical histories relating to these groups are classified in WZ 80.5.

Classification Schedules' Structure and Development

The genesis of the NLM Classification is a Survey Report on the Army Medical Library, published in 1944, which recommended that the "Library be reclassified according to a modern scheme," and that the new scheme be a mixed notation (letters and numbers) resembling that of the Library of Congress. Subsequently a classification committee was formed, chaired by Keyes D. Metcalf and including Mary Louise Marshall who compiled the schedules. Medical specialists acted as consultants to the committee. Based on the consultants' advice, that of the committee and of the NLM cataloging staff, Ms. Marshall produced a preliminary edition of the Library's Classification, which was issued in 1948.

The preliminary edition was revised by Frank B. Rogers and the first edition of the new classification was published in 1951 as the U.S. Army Medical Library Classification. It firmly established the current structure of the classification and NLM's classification practices. The headings for the individual schedules were given in brief form (e.g., WE - Musculoskeletal System; WG - Cardiovascular System) and together they provided an outline of the subjects that constitute the National Library of Medicine Classification. These headings were interpreted broadly as including the physiological system, the specialty or specialties connected with them, the regions of the body chiefly concerned and subordinate related fields. Within each schedule, division by organ usually has priority. All schedules, including some of their sections, are preceded by a group of form numbers representing publication types. These numbers, ranging generally from 1-39, are employed as mnemonic devices throughout the Classification.

Relationship to MeSH

The schedules with their special requirements for use with all types and forms of materials preclude strict adherence to the hierarchical arrangement of the Medical Subject Headings (MeSH), the Library's thesaurus for indexing and cataloging. The schedules maintain their own character in order to provide for material, old as well as new, acquired for the Collection, including dictionaries, atlases, directories and other items, which are not suitable for the arrangements, found in MeSH. However, an effort was made to make schedule headings, subheadings and class number captions compatible with MeSH terminology. The MeSH Tree Structures were used extensively to determine the proper placement of a concept in a schedule and to relate index headings to one another. Since the representation of subjects in the schedules of the NLM Classification is intentionally broad, the captions do not enumerate all of the subordinate concepts that are to be classified in a given number. MeSH descriptors for these subordinate concepts do appear in the index, to the extent practical with appropriate references to the classification numbers.

Index

The Index to the NLM Classification consists primarily of Medical Subject Heading (MeSH) concepts used in cataloging. It includes concepts first appearing in the latest edition of MeSH and other older concepts as warranted by the literature cataloged. It also provides access to classification numbers through these MeSH concepts. Index entries are updated annually to reflect additions and changes of the latest edition of MeSH. For additional information on the Index see About the Index.