A controlled vocabulary is a collection of terms intended to facilitate the uniform description of objects. Controlled vocabularies enable the interoperability of metadata and thus promote the search for and finding of relevant objects. For example, the RADAR Metadata Schema uses controlled vocabularies to assign one or more subject(s) or the language to a dataset. When selecting the controlled vocabularies, recognized standards were used, e.g. ISO standards for the language and country of origin of the research data.