ALL ABOUT: Controlled Vocabulary

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Controlled vocabularies

A controlled vocabulary is an established list of terms for describing people, places, things, and concepts. Many databases use controlled vocabularies for subject terms, form/genre terms, methodologies, and author names.

Controlled vocabularies can be a powerful, though sometimes unintuitive, feature of library databases. Once you know the predetermined label (or controlled term) for a particular topic or person, you can use it to locate all of the materials on that topic or by that author in a single search. It does not matter what words a work uses to identify the author or topic, the official subject heading or author entry will allow you to find it.

Many databases give access to their full vocabulary, often labeled “Thesaurus” or under a “browse” option. 

Note: some databases have no option to browse their controlled vocabularies. In these cases, you can only guess at the right terms. Experiment with labels you find in your results for a simple search: try terms from the detailed view of an item, or from the filter menu options.

More definitions and information:

Types of vocabularies you should know about

Major vocabularies

These are some of the most common and important vocabularies for academic research. There are many, many more out there, and it’s likely that there’s a very specific vocabulary for your field.

Companion vocabularies

Companion vocabularies are developed to complement or correct larger vocabularies. These vocabularies are often developed  in areas related to identities, experiences, and knowledges that have been historically oppressed, ignored, and misrepresented.

Discipline-specific vocabularies

There is likely a vocabulary specific to your discipline. These vocabularies are helpful for tracking details and usages that are specific to the discipline. Typically, it is a national association or other leading organization in the field that maintains and updates the vocabulary.

Controlled vocabularies are works in progress

Controlled vocabularies sound very official, but they are not perfect. They reflect the assumptions and worldviews of the people who made them. Most vocabularies continue to evolve, though the process for updating them can be laborious and slow.

Example: undocumented immigrants and LCSH

With the help of public advocacy, the Library of Congress Subject Headings no longer includes "Illegal Aliens." This story shows how these vocabularies reflect specific decisions that are the products of their time, place, and the authorities that make the decisions. The Wikipedia page for the "Illegal Aliens" heading Links to an external site. summarizes the timeline.

Search for "aliens" in these two versions of LCSH. What do you notice?

Tip: select “LC Subject Headings” from the menu before searching.

How can I find out what controlled vocabulary (if any) a particular search engine uses?

  • At any point: ask a librarian
  • Explore the database’s menus for a “Thesaurus,” “Index,” “Topics,” “Subjects,” or “Browse”
  • Explore the database’s help section or about page for information
  • Search for another website about the database - try databasename subject index OR databasename tips