Ontologies for resource annotation. (A) Overall schematic representation of the key aspects of semantic interoperability in which annotations provide a link between DMR observations and ontology-based meaning. (B) A detail of reference ontology structure representing explicit knowledge. The section of the Biological Qualities ontology only makes use of the subsumption relation. The Anatomy ontology also uses the partonomy relation. Note that, while composite terms have their own unique identifier, they still explicitly refer to Uniform Resource Identifiers (URIs) of standard reference ontologies. In the RICORDO project, both standard reference ontologies and composite terms are formalized in OWL.