Controlled vocabularies are highly useful in data discovery. ISO 19115 offers controlled vocabularies for several metadata elements but for domain specific ones such as keywords it is expected from user communities to come up with their own.

CUAHSI Controlled Vocabulary is prepared to fill this gap. It currently consists of ~2000 keywords that are relevant to hydrologic science and it keeps growing. List of keywords is inspired by several sources such as USGS's Nevada Division of Water Planning Water Words Dictionary, Global Change Master Directory, EPA Storet and NWIS/NAWQA parameter lists. CUAHSI Controlled Vocabulary is available in W3C's Web Ontology Language (OWL) and concepts are linked with broader concept, narrower concept and same as relationships to make inferred search results possible. The following image shows a screenshot of visualization results of the controlled vocabulary using a 3D Hyperbolic tree.