[1] http://docs.oasis-open.org/wsbpel/2.0/wsbpel-v20-rddl.html
[2] http://www.oasis-open.org/committees/download.php/20015/wsbpel-v20-rddl.html
Your link above [2] will not properly resolve the relative links within it to the xsd files.
Use [1] instead.