An abstract parent class for all observation-layer FDOs in a MAC FAIR Digital Twin. Concrete subclasses include `mac:RealWorldOccurrence` (Type 2), `mac:ComputationalPrediction` and its sub-hierarchy (Types 3–6), `mac:ExperimentalObservation` and its sub-hierarchy (Type 7), and `mac:WHOVariantClassification` (Type 8). Every member links to the FDT's anchor (a `mac:SpikeRBDVariant`) via `mac:isObservationOf`. This class is abstract: it carries no direct instances; all instances belong to one of its concrete subclasses.