"export" attribute?

Hi all,

A couple of XML schema questions.

1. Is there any way to say a type is an instance of another type? i.e. Is
there any way to express the concept of meta-class?

2. It seems that "export" attribute was not included in the W3C
recommendation. How can one express a private element to a type (like a
private field in OO paradigm).

Thanks a lot in advance.

Anton