Controlled vocabulary

A controlled vocabulary is an agreed list of terms used to describe and retrieve content, where each concept has one preferred term and the variants are mapped to it. It keeps people and systems from describing the same thing in five different ways.

Kinds of controlled vocabularies

From simple to rich:

1. Synonym ring — terms treated as equivalent for search ("e-stop", "emergency stop", "emergency stop button")
2. Authority file — the preferred names for a set of things, such as product names or organizations
3. Taxonomy — preferred terms arranged in a hierarchy
4. Thesaurus — a taxonomy plus equivalence ("use / used for") and associative ("related term") relations, as standardized in ISO 25964
5. Ontology — classes, relations and rules with formal meaning

Where they are used

• As allowed values of Metadata fields
• As facet values in Faceted classification
• As the terminology behind Labeling systems
• In search, to expand queries with synonyms and improve Findability

In technical documentation

Terminology management and controlled vocabularies overlap: a termbase fixes which term authors write, a controlled vocabulary fixes which term content is classified with. Both reduce translation cost and ambiguity.