There Are Problems Determining If A Model Extension Definition (MED) Applies To Workspace Selection

MED-related actions need to be able to determine if a MED is applicable for their certain situation. For instance, determining if a MED can be added to a selected model. Currently the MED only knows the metamodel URI that it extends and what metaclasses it extends. It does not know anything about model type (physical or virtual). Should the MED also include the model type? Or should the ModelExtensionAssistant be responsible for determining the applicability of it's MED given a certain situation.

Here are 2 scenarios that are causing a problem:

1. The Model MED management dialog is not showing for XML Doc models and should be.
2. The REST MED can be added to non-virtual models.