Non-hierarchical list

The simplest type of controlled vocabularies are non-hierarchical lists of terms, such as a list of countries. Annotating data with these lists makes it easier to filter or search for related records in a database. For example, if you use Europe PMC’s advanced literature search, and filter the results by language, you are choosing from items in a list determined by a controlled vocabulary (Figure 6).

Figure 6. Europe PMC, EMBL-EBI’s literature resource, uses a non-hierarchical list to help you find publications in different languages.