Traits in the Catalog are represented using the Experimental Factor Ontology (EFO, (22)). Supporting semantic tools, the Ontology Lookup Service (23) and Zooma are used to map new traits and provide a consistent and computable representation of traits for users to enhance queries and visualization. Use of EFO also allows the GWAS Catalog data to be interoperable with other datasets as trait annotation is expressed using a formal ontology. Many users map the Catalog's traits to different ontologies. The Ontology Cross Reference Service (OxO) offers mappings to other ontologies, including clinical terminologies such as Snomed-CT (http://browser.ihtsdotools.org/) and the NCI Thesaurus (24) enabling semantic integration of the Catalog's data.
