What are controlled vocabularies?
Answer
Controlled vocabularies are a general term that describes the hierarchical list of categories of topics (also known as subject headings) some databases like Medline, Embase, PsycInfo and CINAHL contain. The controlled vocabulary lists are unique to each database but there are often similarities. In Medline, the controlled vocabulary/subject headings are called MeSH which stands for "Medical Subject Headings". You can view the MeSH subject headings by taking a look at the MeSH Browser and NCBI MeSH. However, not all subject headings are called MeSH - in Embase, they are called EMTREE terms and in CINAHL, they are called CINAHL Subject Headings.
In the past, a human would read the full-text of an article when it was being processed for indexing in a database, and that person would apply the applicable subject headings (aka controlled vocabulary) to that article record. However, subject headings are increasingly being assigned to articles using AI, which is not always accurate. In other words, articles would be categorized in the database based on its applicable subject headings, which reflect the content within that article.
We can liken subject headings to #hashtags in social media, where they often capture the "essence" or main ideas and themes of the content presented. However, unlike hashtags used in social media, we can't create our own subject headings, as these exist in the hierarchy of terms in a controlled vocabulary.