Why have SpeciesType and CompartmentType disappeared in Level 3?
In reality, SpeciesType in SBML Level 2 was a construct intended to support the ability to define “generalized reactions”, as well as multicompartment entities. The idea of generalized reactions is to allow easy definition of reactions that take place in different compartments but otherwise are identical; this is essentially the concept of rule-based reactions of a sort found in systems such as BioNetGen. However, while SpeciesTypes and CompartmentTypes were accepted for introduction in SBML Level 2, the SBML community rejected the introduction of generalized reactions. Thus, the primary purpose of the SpeciesType construct was never realized. Moreover, it also turned out that in the 4 years of the existence of SpeciesType and CompartmentType in Level 2, very little software support was developed for them. As a result of these considerations, during the development of SBML Level 3, it was decided that these constructs did not belong in Level 3 Core, and any such constructs should be mo
