About Taxonomies & Controlled Vocabularies / quote 4 of 4
Thesauri and their three kinds of relationship
A thesaurus, as used in information science and literature retrieval, is essentially a controlled vocabulary following a standard structure, where all terms in the thesaurus have relationships to each other. These relationships are typically of three kinds: hierarchical (broader term/narrower term), associative (see also), and equivalent (use/used from or see/seen from). In addition, it is common in thesauri that some or all terms have scope notes, brief explanations of how the term should be used in indexing. Term history notes may also be present.
Thesauri are most often used in indexing periodical literature, especially over a period of time. Detailed thesauri have been created for specialized subject areas by publishers of periodical indexes. Often the thesauri themselves have become published works for purchase.