XML and Geometry

Hi,
Do we have any published XML schema for representing geometry of CAD
such as curves and surfaces (NURBS)?
If yes, can someone let me know where I can find the material.
Thanks,

Prakash Reddy Bande
email Prakash.Bande@sdrc.com
Ext.124,Ph.+91-2139-33666
Structural Dynamics Research Corporation
Product Groups - India