Subject Headings and Index Terms
Since most resources contain information on a number of different subjects, library users need more comprehensive subject access to information than can be provided by the broad categories of a classification system.
Consistent vocabulary is also needed to describe what a book or article is about. Online catalogs use subject headings for books. Periodical indexes use index terms for articles. Unfortunately, these are not always in agreement.
Both subject headings and index terms are carefully assigned by a librarian or indexer to describe content. Subject headings and index terms are designed to facilitate comprehensive searching by topic.
Library of Congress Subject Headings
Not only has the Library of Congress developed a classification system to organize its books by subject on the library shelves, it also developed a subject heading system to describe what a book is about.
Library of Congress Subject Heading volumes are located in the Reference Department. Each heading has its own listing and includes similar, broader, and narrower headings which may also be applicable to your search. A Library of Congress Subject Heading is part of an interconnected list of related subject headings, something like a family tree. In fact, the phrase "subject tree" is used to describe these related subject headings. To make an item as accessible as possible, multiple subject headings are assigned.
Because a book has been assigned subject headings, patrons can use those same subject headings to search the library catalog to find other books about the same subject. This effective technique of using subject headings to search for similar material is one of the most important and productive skills you can learn and use. (We will demonstrate how to search the library catalog in Lesson 4)
Index Terms for Periodical Articles
You use a library online catalog to find books and periodicals the library owns. To find magazine and journal article citations, you use finding resource called an index. Companies that index magazine and journal articles tend not to use the Library of Congress Subject Headings. Rather, they create subject heading systems of their own. The headings used to describe the subject matter of individual periodical articles are called index terms, descriptors, or controlled vocabulary.
The index terms used to effectively search in a periodical index or database are often made available to online searchers in a thesaurus. A thesaurus is an alphabetical listing of definitive subject terms used in a particular periodical index or database. It also lists synonyms for each term and indicates relationships between terms.
A database thesaurus often includes definitions, or notes explaining the use of a term in the particular database. When a term is not used in the database, there are often suggestions for terms that are. Using controlled vocabulary in your search will help insure that you retrieve all the records relevant to your topic.
We have print thesauri for many of our indexes and databases. Most electronic indexes have online versions of their thesauri that you can use to construct your search.
Locations in the Library
Libraries arrange their materials into different collections based on the type of resource. It will be helpful for you to know about these collections.