Clearly, in a realistic representation of acquisition and creation scenarios, a «twin»
DigitalTwincan't have an assigned «physical»
@Entityuntil they are created. However, in most diagrams in the following trail, the multiplicity of 'digitalEntity:@Entity' and 'physicalEntity:PhysicalEntity' within «twin»
DigitalTwinis given as  (rather than [0..1]) to drive home the idea that a well-formed «twin»
DigitalTwinalways eventually has exactly 1 assigned «physical»
oclInStateand Constraints, but that would only be clear to OCL-aware readers.