Running OpenCDISC on Define only

Hi, I've run openCDISC many times on xpt files with and without the define document.  I'm being asked to run OpenCDISC on the define.xml only (no corresponding xpt files).  Does this make sense?  If so, how would I do that?  the OpenCDISC validator doesn't seem to want to start when I just plug the define.xml in without the xpt files.

thanks!

PDL