The term “controlled vocabulary” is often used interchangeably with thesaurus and taxonomy. However, there are slight differences among the three. In a nutshell, a controlled vocabulary (CV) is a set of terms that are used to identify key elements of a document so it can later be found via browse or search. There are several types of controlled vocabularies.
An authority file is a non-hierarchal set of preferred terms. It may also contain synonym rings of variant terms.
A taxonomy is a set of authority files plus a hierarchal arrangement of broader terms (BT) and narrower terms (NT).
A thesaurus is a taxonomy with the addition of related terms (RT).
An index is a controlled vocabulary created from and used for a specific document. A subject index is a thesaurus and locators. A name index is an authority file and locators.
The indexing process and thesauri development are very closely related. Indexing is both an art and a science. The indexer is always considering the voice of the author and the needs of the reader. Typically an indexer will work on a stand-alone index that may be updated in later editions. Thesauri development is much like indexing but is often an open-ended process involving a database of information. A thesaurus requires maintenance as new material is incorporated into the database.