Introduction to Taxonomies and Thesauri

Heather Hedden, Senior Vocabulary Editor, Indexing and Vocabulary Services for Gale/Cengage Learning led a session on “An Introduction to Taxonomies and Thesauri” on Friday, June 17, 2016 at the American Society for Indexing/Indexing Society of Canada Annual Conference in Chicago.  Taxonomies and thesauri are types of controlled vocabularies that include an authoritative, restricted list of terms (words or phrases) mainly used for indexing/tagging content to support retrieval.  They usually make use of equivalent non-preferred terms (synonyms, etc.) to point to the correct, preferred terms, and may or may not have structured relationships between terms.


A taxonomy is a controlled vocabulary with broader/narrower (parent/child) term relationships that include all terms to create a hierarchical structure.

  • With focus for categorizing and organizing concepts
  • May or may not have equivalent non-preferred terms (synonyms, etc.) to point to the correct, preferred terms
  • May comprise several hierarchies or facets (A facet can be considered a hierarchy.)

A taxonomy is any kind of controlled vocabulary in an enterprise, corporate setting, content management system, or for website navigation (e.g. e-commerce site).


A thesaurus is a controlled vocabulary that has standard structured relationships between terms.

  • Hierarchical: broader term/narrower term (BT/NT)
  • Associative: related terms (RT)
  • Equivalence: preferred term (“use for” or “used for”)/non-preferred term (use) (USE/UF)

Also supports notes, such as scope notes (SN), for terms, as needed.

A thesaurus is most often the kind of controlled vocabulary used in indexing periodical literature.  It is also used for literature retrieval databases.  It is used by librarians, indexers, or other information professionals.  It includes non-preferred terms.


The benefits of taxonomies/controlled vocabularies are that they bring together different wordings (synonyms) for the same concept.  They help people search for information by different names.  By classification, they help organize information into a logical structure.  They help people browse or navigate for information.

In future blog postings I will discuss other sessions from the American Society for Indexing Annual Conference in Chicago.  For more information about the services provided by the author of this blog, see the Stellar Searches LLC website,

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