subtyping and XSDs

Hi all.

My name is Jesper Bengtson and I am a PHD-student at the University of
Uppsala, Sweden. I am currently searching for a tool which can determine
wether an XSD expresses a subtype of another XSD, i. e, can any
XML-document which is accepted by XSD1 also be accepted by XSD2. The
reverse need not hold.

I have been searching the web and some xml groups for such a tool but not
found much. Does anyone know if such a tool exists? If not, I will have to
write one myself.

I am greatful for any insights.

/Jesper Bengtson