A Distribution_domain is either a Scale or a Parameterisation.
NOTE - Either a Scale or a Parameterisation can be referenced as domain by an Identification_of_property_distribution.
A Parameterisation is referenced if the Property_distribution has a Design_feature_space or Activity_or_state_space as its domain.
A Scale is referenced if the Property_distribution has a Property_space as its domain.
EXPRESS specification:
*) TYPE Distribution_domain = SELECT (Parameterisation, Scale); END_TYPE; (*