A subset of ontology classes and properties for connecting rare disease data in the context of creating FAIR rare disease data 'at the source'. The aim is to facilitate data annotation at the source in order to enable questions and analysis across rare disease resources (e.g. biobanks, registries, molecular data). I.e. the model is not meant as a new conceptualization. Ontology files: 1. rdc-core: the minimal set of classes and properties to map to the data in the sources of the platform. RD core represents little more that the lowest level types for the identifiers of the sources of the Rare Disease Connect platform. 2. rdc-meta: the minimal semantic model, defined as much as possible using existing ontologies (OBIB, etc.). 3. rdc-meta-extended: this model includes the subclasses and properties of the entities that were imported from source ontologies, i.e. when you use the ‘move’ function of protege, rather than just copy the URI. 4. rdc-thesaurus: mappings to ‘concepts’. A SKOS-based thesaurus represents a ‘light-weight’ ontology. This allows us to define in simple terms the relations between similar or equal terms in different terminologies. 5. rdc-mapping: mapping between models, for instance between the SKOS concepts and RD-core and RD-meta. 6. rdc-example-instances: example instances (‘individuals’) to show the model at instance level. The instances, especially the IDs relate to actual data in data sources. Their datatype properties link to data.