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The University of North Carolina at Chapel Hill

What's Library of Congress
Subject Headings?

The Library of Congress subject headings system was originally designed as a controlled vocabulary for representing the subject and form of the books and serials in the Library of Congress collection, with the purpose of providing subject access points to the bibliographic records contained in the Library of Congress catalogs.

As an increasing number of other libraries have adopted the Library of Congress subject headings system, it has become a tool for subject indexing of library catalogs in general. In recent years, it has also been used as a tool in a number of online bibliographic databases outside of the Library of Congress.

A subject heading may consist of one or more words. A one-word heading represents a single concept, whereas a multiple-word heading may represent a single concept or multiple concepts.

A subject heading representing a single concept may appear as a single word or a multiple-word phrase, usually an adjectival phrase but occasionally a prepositional phrase. Each such heading represents a single object or idea (Examples include: Automobiles, Botany, Budget deficits, Electric interference, Boards of trade, Clerks of court).
LCSubject Heading sample

The Library of Congress (LC) subject headings are used to find information by keywords in libraries in the United States. The red, four-volume Library of Congress Subject Headings (LCSH) set is an important guide to finding the keyords to use in the SUBJECT search option in the UNC-CH Online Catalog, or the UNC-CH Online Catalog Services.

By looking in the LCSH you can often avoid frustration, save time, and locate useful terms that might not have occurred to you.

On the left is a sample from the LCSH.
See below for an explanation of its use.

  • Headings in boldface may be used for subject searching. For example, "Models and modelmaking" may be used as a subject heading.
  • May Subd Geog. Place names may follow the heading.
  • Call number given (TT154) indicates where most books on this subject are found. Rather than search further, you might just go directly to this call number.
  • UF (Used For) refers to headings which are not used.
  • BT (Broader Topic) refers to more general subject headings. These headings would be useful if you need to broaden your topic.
  • RT (Related Topic). These terms can provide ideas of other topics to investigate.
  • SA (See Also) refers you to other ways of looking up the same topic.
  • NT (Narrower Topic) refers to more specific headings than the boldface heading.
  • -- (a dash) refers to a subdivision of the boldface subject heading. These listed subdivisions are useful for narrowing a topic.

Types of Relationships within Subject Headings

Pre-coordinated Relationships

A pre-coordinated multiple-concept heading contains two or more otherwise individual or independent concepts coordinated or related through one or more linking devices. Pre-coordination results in phrase headings or main-heading/subdivision combinations. Examples include: Budget in business, Church and industry, Earth-Rotation, Biology-Scholarships, fellowships, etc.

Term relationships

Three types of relationships are represented in the cross- reference structure of Library of Congress Subject Headings: equivalence, hierarchical, and associative. These relationships are expressed in terms of USE, UF (Used for), BT (Broader term), NT (Narrower term), RT (Related term), and SA (See also) references. Each reference links a term or heading with another heading or with a group of headings..

Equivalence relationships

USE references are made from unauthorized or non-preferred terms to authorized or valid headings. Reciprocals, in the form of UF (Used-for) references, are made under the valid headings. The referred-from terms include synonyms in direct and inverted word order, alternative spellings (including singular and plural forms), alternative endings, changed or canceled headings, and abbreviations and acronyms. For phrase headings entered in the inverted form, USE references are made from the straight form. For phrase headings entered in the straight form, USE references are made from the inverted form in selective cases. For compound headings and for topical headings subdivided by other topics, USE references are made from the reversed form, thus bringing each significant term to the initial position. Occasionally, USE references are made to broader headings from narrower terms not used as valid headings. USE references are not generally made from equivalents in foreign languages. Examples

Hierarchical relationships

Headings related hierarchically are connected by means of reciprocal BT (Broader term) and NT (Narrower term) references. A heading is linked to the level immediately above it and the level immediately below it in the appropriate hierarchy. Types of hierarchical relationships include Genus/species (or class/class member), Whole/part, and Instance (or generic topic/proper name example).

Broader terms

Under each valid heading, other headings representing concepts on a level immediately above in the hierarchy are listed as BT (Broader term), except when the heading in question represents the "top term" in the hierarchy, or when the broader term cannot be readily identified. Other exceptions include headings for geographic regions, family names, and inverted headings qualified by names of languages, nationalities, ethnic groups, or terms that designate time periods, when the only appropriate BT is the identical heading without the qualifier. When a heading belongs to more than one hierarchy, multiple BT references may be made. In complex situations such as compound headings, prepositional phrase headings, and headings with subdivisions, BT references not representing true hierarchical relationships are made in selective cases.

Associative relationships

Headings related in some manner other than by hierarchy are linked with RT (Related term) references. Such references may be made for the following types of relationships: headings with meanings that overlap to some extent, headings representing a discipline and the object studied, and headings representing persons and their fields of endeavor. Examples: Ships RT Boats and boating Birds RT Ornithology Medicine RT Physicians

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