A controlled vocabulary that displays only the hierarchical relationships of all its terms. Users can follow related terms from broad to specific to find the term or subject they are looking for. 

Taxonomies

A controlled vocabulary where associative, equivalence, and hierarchical relationships are displayed between the preferred terms. Users can see preferred and non preferred terms, the hierarchical relationship between terms, and terms that overlap but are not in an equivalence or hierarchical relationship. 

Thesauri

A simple collection of terms with narrow definitions. These are generally used for small collections of terms like a drop-down menu on a webpage. These do not display relationships between terms.

Controlled Vocabulary Lists

A set of terms  that share the same definition. These are generally used for information retrieval in a system without an accessible controlled vocabulary. They are used so that a search term will pull results for terms with the same or similar definitions. 

Controlled Vocabulary Synonym Rings

- Lists
- Synonym Rings
- Taxonomies
- Thesauri

San Jose State University

A list of subject headings that are used along with metadata to sort and organize resources in a library or archive. The collection of terms are used to describe documents and content objects.

Controlled Vocabularies 

ANSI/NISO. (2005). Guidelines for the Construction, Format, and Management of monolingual Controlled Vocabularies. American National Standards Institute. https://groups.niso.org/higherlogic/ws/public/download/12591/z39-19-2005r2010.pdf 

Guidelines for the Construction, Format, and Management of monolingual Controlled Vocabularies

Types of Controlled Vocabularies

The operation of selecting preferred terms or headings which are used to describe the content and characteristics of an information object. 

Indexing

The selection of terms for a controlled vocabulary is important for usability. Selection cannot be arbitrary and there are several considerations that need to be taken into account. 

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