Thesauri and Subject Indexing
Subject indexing enables the searching machine-readable catalogues by indexed topics. In order to retrieve the most appropriate bibliographic records, each record is indexed with one or more subject terms (e.g. 'Music', 'Evolution', 'Africa' or 'Mount Everest').
Over the years, a number of sets of such terms (also known as thesauri or taxonomies) have been devised for subject indexing. These have been used in a variety of finding aids (e.g. catalogues, indexes, and inventories), and are kept up to date by constant or regular revision of the schemes.
A formal definition of a thesaurus, is:
These are the two main parts of the Thesaurus; index terms (1) and term relationships (2). The index terms are the individual words, terms, or phrases. When terms are ambiguous, a "scope note" can be added to ensure consistency, and give directions how to interpret the term. The term relationships are links between the terms. Synonyms, and other useful relationships between terms, are called related terms (RT). Broader Terms (BT) generalizes a term and Narrower Terms (NT) is a specialization.
Although the range of collections in archives, libraries and museums means that any one term set might not be appropriate for all, enough thesauri have now been developed that it is best practice to use a recognised scheme that already exists, rather than devising yet another set. The content scope of the collection and its curatorial domain will both influence the choice of scheme. For example, a library might choose the Library of Congress Subject Headings, an art gallery the Art & Architecture Thesaurus and an archive the UK Archival Thesuarus.
Medical Subject Headings (MeSH)