EVL (as all Epsilon languages) are intended to work on a model, and usually models conform to a metamodel. In the case of EMF, models are xmi files that conform to a model in an ecore file. Papyrus is build a top EMF, and thus uses ecore metamodels. Papyrus stores the model in a xmi file with a ".uml" extension. Thus if you want to use EVL (or any other epsilon language on papyrus models) you will use the eml file as the model and the appropriate metamodel (it depends whether if the model is a UML, SysML, MARTE, etc.).For example the metamodel for a SysML model is "http://www.eclipse.org/papyrus/0.7.0/SysML".