Ontologies are special types of data that are often referred to as standard metadata. They serve as metadata standards that can be used for the definition, annotation (labeling), indexing, linkage (mapping), extraction, integration, retrieval, enrichment, harmonization, and interaction of data. Ontologies, sometimes defined as shared conceptualization of a domain represented in a formal language, represent not only the concepts used across scientific work, but just as importantly, the relationships between the concepts.