The extension of SBML Level 3 Core's Model class is relatively straightforward: the Qualitative Models Package adds two lists, one for holding qualitativeSpecies (ListOfQualitativeSpecies), and the other for holding transitions (ListOfTransitions). The Model element may contain at most one ListOfQualitativeSpecies, which must contain at least one QualitativeSpecies. It may also contain at most one ListOfTransitions which must contain at least one Transition.