The current importer only allows one graph to be imported per file. It would be convenient if the importer would allow (one of) the extensions to generate one or more graphs (or other resources) on its own, instead of the exporter itself probing for the various graph types and picking one.
Likewise, the exporter only allows the current graph to be exported, but does not have access to other graphs/the rest of the grammar. This would help for example when exporting a host graph and reading the type graphs for some of the structure.
Some use cases:
Import Ecore model: requires generation of type and rule graphs
Import Ecore instance model: requires generation of (single) host graph
Import GXL instance model: requires generation of type, rule and host graphs (everything is possibly in one file)
Export instance graph to ecore instance model: requires exporting host graph for objects and reading type graph+rule graphs for model information.