This class represents the main resources defined by the Simulation Data Model in the same way as the Registry/Resource class represents resources in registries. It is the base class of specialisations SimDM/Protocol, SimDM/Experiment, SimDM/Project and SimDM/Service.
These resources are the root entities that would get registered in a Simulation Database for example. They are also represented by root element declarations in XML schema serialisations of the model.  
This class is a thin copy of the Registry/Resource and borrows some of its elements. It *is-not-a* Registry Resource in the sense of inheritance. In particular a SimDM/Resource has a more refined and targeted content model. Also, SimDM/Resource-s are in general (much) more fine grained than Registry/Resource-s and would not qualify to be registered in an IVOA Registry.
It will howevere be possible to transform certain SimDM/Resource-s into Registry/Resource-s.