Identifying Subject Headings as Primary or Secondary

• Optionally, libraries may choose to follow NLM practice and identify topical subjects as either primary or secondary headings via MARC coding (cf. Module 4, MARC Coding)


• The primary heading(s) represent the main topic of the item being cataloged and will lead the cataloger to, and correspond with, the classification number to be assigned


• Prefer one primary subject per item, unless the main topic cannot be adequately covered by one primary descriptor (or descriptor/qualifier combination)
  Example:
  
  • A work on fire prevention in hospitals would require the coordination of the MeSH descriptors Hospitals and Fires (with the qualifier prevention & control) to get to the appropriate NLM Classification number of WX 185. Therefore both of these subjects would be treated as primary. (Cf. Fundamentals of the NLM Classification, Module 4—General Principles)
  
  
• All other topical subjects are identified as secondary subject headings
  Example:
  
  • A work on acupuncture for chronic low back pain would have the primary subject Low Back Pain (with the qualifier therapy) and secondary subjects for Acupuncture Therapy and Chronic Disease, since NLM prefers to classify by disease, regardless of special emphasis on diet, drug, therapy or diagnostic procedure