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User manual:
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To use the GrGen.NET's XMI exporter, we have to use the graphs auxtypes.gm, L3.gm and L3Metamodel.gm.
The auxtypes declares nodes that are used to compute unique ids for the graph elements to be exported.
The automatically produced L3.gm defines the graph model representing the complete UML (it is generated by 3_umlGraphmodel).
L3Metamodel.gm is distilled from the actually used MOF modeling elements in the UML for reflection purposes (it is generated by 6_cmofGraphmodel).
The script newproject1.grs produces an example graph using the GrShell.
It is generated automatically by 4_umlGraph from an XMI file generated for example by Altova UModel 2008.
The script L3Metamodel.grs represents the UML metamodel for reflection purposes.
It can be loaded by the GrShell, too.
Please note that this does not have to happen (UML graphs can be transformed without using the metamodel; nevertheless our exporter needs this information).
The rule file g2x.grg exports a UML graph back to XMI, so the round-trip is complete.
The script g2x.grs is an example for reading a UML graph encoded as a script (newproject1.grs) and exporting it to XMI.
This trivial example does actually no transformation on the UML graph.

KNOWN BUGS:
           Some properties are not written back to XMI (in XMI lowerValue, upperValue, ...). So the output is mising some data.