NLM's Subject Headings Differ in LocatorPlus and OCLC
Question: Why are NLM's LocatorPlus subject headings different from NLM's subject headings found in OCLC records?
With the implementation of the Voyager Integrated Library System, the Cataloging Section harmonized its practices for subject heading content and structure with NLM indexing practices.
These changes are intended to facilitate cross-file searching and enhance retrieval by assuring that the same terms produce like results for articles, books, nonprint materials, electronic resources, etc.
NLM subject headings in LocatorPlus records follow the indexing pattern:
- the 650 contains only main headings or main headings and topical subheadings
- the geographic qualifiers are in the 651 field
- publication types (PTs, aka form divisions) are in the 655 field
When NLM distributes these records in the MARC format, a program recombines the appropriate headings into a precoordinated string:
650 _2 $a Main heading $x topical subheading $z geographic $v publication type $x language
The language subfield, taken from coded data in the 041 field, is only appended to the 650 subject string as subfield $x when one of the following publication types is used in the record: Dictionary, Encyclopedias, Phrases or Terminology.
Instructions on how to create a precoordinated subject string from a LocatorPlus record:
Instructions on how to create a faceted subject display from an OCLC record: