Definition: A Reference Model is an information model which defines a rigorous and stable set of modelling patterns upon which the clinical models (i.e. archetypes) are defined. Modelling patterns defined in the CIMI reference model include a set of complex datatypes, information patterns (e.g. data, qualifier, state), and structural patterns (e.g. composition, entry, tree). All clinical models (i.e. archetypes) will be defined by constraining the reference model. The reference model is intended to be instantiated with patient data, which conforms to the constraints defined by the associated clinical model.