ABSTRACT
Lists of subject headings, bibliographic classification schemes, and thesauri are the major types of controlled vocabularies, and all such vocabularies are subsets of the lexicon of a natural language. Vocabulary control is the process of organizing a list of terms (a) to indicate which of two or more synonymous terms is authorized for use, (b) to distinguish between homographs, and (c) to indicate hierarchical and associative relationships among terms in the context of a thesaurus or subject heading list (National Information Standards Organization [NISO], 1994). Subject headings in alphabetical order were the earliest attempts to control vocabulary or provide an authority list for use in subject catalogs and printed indexes. The terms in the lists were often precoordinated for multiple and related concepts, and this is a characteristic of subject headings that distinguishes them from thesaurus descriptors (Coates, 1960; Foskett, 1982; Pettee, 1946; Roberts, 1984; Spärk Jones, 1972). An authority list gives the subject headings established for a particular catalog and the cross-references necessary to lead a user to the preferred heading.
