Schema redefintions in cascade

Dear all,

I am changing an existing schema using the "redefine" tag. The original
schema file is left untouched. As some elements must be both restricted and
extended, I have created two schema files. The first one redefines the
original schema file restricting some elements and the second one redefines
the restricting schema file adding some extensions. An element existing in
the original file can be restricted in the first file and then extended in
the second one.
It works fine in XML Spy - it has a proprietary schema validator - but it's
not working fine in other systems such as Saxonica, Stylus Studio, Xerces or
Oracle's schema validator. I think nested redefines (or includes) can be
done according to the W3C Schema recommendations. 

I would like to know if my approach is correct and if there is another way
to achieve the same results. Any suggestion to solve this issue is more than
welcome.


Thank you very much.

Kind Regards,
Leo Antoli