Subject heading

Subject heading is a word or phrase from a controlled vocabulary which is used to describe the subject of a document or a class of documents. Subject headings may be represented in individual bibliographical records or they may just exists in classification systems or as separators in card catalogues.


Wellisch (1995, p. 479) writes that indexers before the advent of thesauri relied on lists of terms variously known as subject heading lists, keyword lists, term lists, and similarly labeled aids to consistency in indexing, and he found that:


"Most subject heading lists were and still are modeled on the most extensive and best-known on, the Library of Congress Subject Headings (LCSH) (Library of Congress 1989- ), and are characterized by the fact that they are much more loosely structured than thesauri and are, therefore, less effective for indexing or searching. . . ." (Wellisch, 1995, p. 479).


Wellisch characterization of subject headings seems to be very much a characterization of LCSH and less of subject headings as a kind compared to thesauri. It is important to remember that thesauri were developed in the culture of electronic databases based on post-coordinative indexing and mainly based on journal articles, whereas subject headings were mainly developed for paper-based, pre-coordinative indexing systems. The subject headings Wellisch is talking about were developed for indexing monographs/books but other kinds were developed for subject bibliographies. Also: Both subject heading systems and thesauri may be high-class or of a poor quality. Wellisch's serious critique of subject headings (which are not quoted in full above) may be a critique that is not valid for all subject headings.


Thesauri were introduced as much smaller systems than subject headings due the post-coordinative principle. Compound terms (cf. indexing phrase) were split into single words (cf. UNITERM), whereas subject heading systems to a much larger degree use compound headings. 


Library of Congress Subject Headings (LCSH) are assigned by the Library of Congress to American books and via exchange of MARC-records searchable in many libraries in the world, including some Danish libraries. Larson (1991) found that these subject headings have a low specificity, why many users preferred not to use them when searching OPACs. Denda (2005) also found that "the relevance and usefulness of controlled vocabularies such as the Library of Congress Subject Headings in emerging interdisciplinary fields and the suitability of conventional library tools for organizing and accessing digital information are in question."


Gerhard, Su & Rubens (1998) reported an investigation of the assignment of subject headings to core works in women's studies. Annotations for the works were compared with subject headings on OCLC cataloging copy, mainly created by the Library of Congress. Inadequacies were identified and traced to three sources: inadequacy of terminology, the complexities of assigning headings in interdisciplinary and/or emerging fields, and standard cataloging practices. Recommendations for amelioration of these problems were made.


It is often possible to increase recall in an (older) database considerably by verbalizing coded subject headings and make them searchable. Often they have a low specificity why precision tend to be critical low. In spite of this may such verbalized codes serve a purpose in Boolean searches as ways of limiting too broad searches.


Carmichael (2002) downloaded 18,757 records listed under the subject headings "Homosexuality," "Gay Men," and "Gays" from WorldCat, OCLC (records for "Lesbian" and "Lesbians" were not examined). Findings of the study suggest that while there has indeed been considerable growth in the quantity of gay literature produced since 1969, such gains may be offset by the deteriorating quality of cataloging copy, which makes the experience of browsing records a discouraging and confusing one.


Garrett (2007) reports on an experiment at Northwestern University Library to add subject headings to online records for the Eighteenth Century Collections Online (ECCO). The author assesses the benefits of this enhancement by using a representative research topic. The paper argues in two directions: first, by considering the importance of subject headings for access to historical materials; and, second, by examining the value added by subject headings even when the full text of a work is available online.





Browne, G. (1992). Scope notes for LISA subject headings. Online Review, 16(1), 3-16. 


Carmichael, J. V. (2002). Effects of the gay publishing boom on classes of titles retrieved under the subject headings "Homosexuality," "Gay men," and "Gays" in the OCLC WorldCat database. Journal of Homosexuality, 42(3), 65-88.


Chan, L. M. & VizineGoetz, D. (1997). Errors and obsolete elements in assigned Library of Congress subject headings: Implications for subject cataloging and subject authority control. Library Resources & Technical Services, 41(4), 295-322.


Christ, J. M. (1972). Concepts and Subject Headings: Their Relation in Information Retrieval and Library Science. Metuchen, N. J.: Scarecrow. Press.


Denda, K. (2005). Beyond subject headings: A structured information retrieval tool for interdisciplinary fields. Library Resources & Technical Services, 49(4), 266-275. 


Drabenstott, K. M.; Simcox, S. & Fenton, E. G. (1999). End-user understanding of subject headings in library catalogs. Library Resources & Technical Services, 43(3), 140-160.


Drabenstott, K. M. & Vizine-Goetz, D. (1994). Using Subject Headings for Online Retrieval: Theory, Practice, and Potential. San Diego: Academic Press.


Drabenstott, K. M. & Williams, M. (1999). Do librarians understand the subject headings in library catalogs? Reference & User Service Quarterly, 38(4), 369-387.


Eddison, B. & Batty, D. (1988). Words, words, words—descriptors, subject headings, index terms. Database 11(6), 109-113.


Garrett, J. (2007). Subject headings in full-text environments: The ECCO experiment. College & Research Libraries, 68(1), 69-81.

Gerhard, K. H.; Su, M. C. & Rubens, C. C. (1998). An empirical examination of subject headings for women's studies core materials. College & Research Libraries, 59(2), 130-138.


Larson, R. R. (1991). The Decline of Subject Searching: Long-Term Trends and Patterns of Index Use in an Online Catalog. Journal of the American Society for Information Science, 42(3), 197-215.


Miller, J. & Sears, M. E. (Eds.). (2004). Sears list of subject headings.18th edition. New York: H. W. Wilson Co.


Weinberg, B. H. (1997). Review of Drabenstott & Vizine-Goetz (1994): Using Subject Headings for Online Retrieval: Theory, Practice, and Potential. Library Resources & Technical Services, 41(1), 60-67.


Wellisch, H. H. (1995). Indexing from A to Z. 2nd. ed. New York: H. W. Wilson.


Winkel, L. (Ed.). (1994). Subject Headings for Children. Albany, New York: Forest Press.




See also: Library of Congress Subject Headings; Medical Subject Headings; Metadata; Sears list of subject headings; Subject access points





Birger Hjørland

Last edited: 08-01-2008