Schema to verify validity of responses to ListSets OAI-protocol request. This Schema validated at http://www.w3.org/2000/09/webdata/xsv on 2001-01-19 with XSV 1.173.2.15.2.4/1.74.2.25 of 2001/01/03 19:13:19