In Kermeta 2, in order to delegate the resolution work to the tool, it use a specific internal structure based on Unresolved metaclass. The resolver will transform every Unresolved into the final real ModelElement. This allow to build transformations that generate valid km models without the difficulty of dealing with the framework default types and the resolving of km model splitted in several files. All Kermeta 2 internal transformations like kmt2km, ecore2km, qvt2km use this mechanism.