The Library of Congress maintains two separate authority files: one for names and one for subjects.
LC name authority file
LC staff and NACO participants create headings for personal, corporate, conference and geographic names, as well as uniform title and
LC subject authority file
LC creates records for headings and heading subdivision combinations included in Library of Congress Subject Headings (LCSH). LC does not necessarily create a record for every unique heading subdivision combination assigned to a bibliographic record.
Categories not included in LCSH
Because LCSH excludes the following categories of headings, LC creates no subject authority records for:
- Names of persons, unless used as a pattern or example, or unless a subdivision must be displayed
- Names of corporate bodies and jurisdictions, unless used as a pattern or example
- Headings incorporating free-floating subdivisions, unless a reference or the record was issued for subject heading validation purposes
- Phrase headings created by incorporating free-floating terms (e.g., Region, Valley, in art, in literature)
LC creates and distributes name authority records for the first two categories.
Scope of the subject authority file
The subject authority file does not contain records for non-LC authority systems such as MeSH (Medical Subject Headings), NAL (National Agricultural Library), and LAC (Library and Archives Canada).
LC authority record prefixes
LC assigns authority record control numbers (LCCNs) to all authority records. The control number consists of an alphabetic prefix
plus eight or ten digits. The alphabetic prefix indicates which system created the authority record.
|nb - for name headings
dg - for demographic terms (LCDGT)
gf - for genre/form terms (LCGFT)
mp - for medium of performance terms (LCMPT)
n - for name headings
sh - for subject headings (LCSH)
sj - for subject headings for children (CSH)
|no - for name headings
nr - for name headings
|ns - for name headings
Unique characteristics in LC records
LC subject records may contain the following unique characteristics:
- LC subject-authority records do not carry narrower term references.
- Source data information (e.g., 670 fields) may not be present in all existing authority records. However, newly created records usually carry source data.
Former headings used as cross-references
The LC subject authority file contains only headings and cross-references from the current edition of LCSH, its supplements, and weekly lists. Cross-references that link subject headings formerly used to their current forms may or may not be present.
Geographic subdivision practice
Topical subject headings (field 150) and topical subdivision headings (field 180) do not always support subdivision by place.
To indicate that field 150 and/or field 180 may be subdivided geographically, the fixed-field element Geo subd contains code i.
Code n or a fill character, █ in Geo subd indicates that the heading in field 150 and/ or field 180 may not be subdivided geographically.