Hey George

You were perfectly right! That's exactly where I went wrong!
Thank you very much...

(I have to admit to myself, that a fool with a tool* is still a fool )

*(Even if the tool is almost fool-proof)

After having bought the Oxygen5.1 License, I tried to create a simple schema and according to it an xml-file. But I always got the same error: Identity Constraint error: identity constraint "KeyRef@..." has a keyref which refers to a key or unique that is out of scope But validated with XM...