What are the different schema languages?

I'm trying to compile a list of all the different XML schema languages and
their specifications out there and can only think of a handful:

 - XML 1.0 Document Type Definition (DTD) found at
http://www.w3.org/XML/1998/06/xmlspec-report-19980910.htm
 - W3C's XML Schema Definition (WXS or XSD) found at
http://www.w3.org/XML/Schema
 - Oasis' RELAX NG found at http://www.oasis-open.org/committees/relax-ng/
 - Microsoft's XML Data Reduced schema (XDR) found at
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/xmlsdk30/ht
m/xmconxmlschemadevelopersguide.asp

Are there any others that I am unaware of?

-BKN