In SBML spec, there is a definition of 'species':
Species: A pool of entities of the same kind located in a compartment and participating in reactions (processes). In biochemical network models, common examples of species include ions, proteins and other molecules; however, in practice, an SBML species can be any kind of entity that makes sense in
the context of a given model.
We do not have it in SBGN PD spec while the term is used a few times.
A more general question is about best practices of spec development, maybe aligning the language of SBML and SBGN specs.
The term `specie' in the SBML specification Level 1 was an error. The singular form of species is also species. This has been corrected relatively early.
In SBML spec, there is a definition of 'species': Species: A pool of entities of the same kind located in a compartment and participating in reactions (processes). In biochemical network models, common examples of species include ions, proteins and other molecules; however, in practice, an SBML species can be any kind of entity that makes sense in the context of a given model. We do not have it in SBGN PD spec while the term is used a few times. A more general question is about best practices of spec development, maybe aligning the language of SBML and SBGN specs.