Just a quick follow up: its probably clearer to look at the brief talk on this software that I gave at the last IVOA in the Query group..here's a link to the talk (note this was in early days the software used to be refered to as "ORML") http://www.ivoa.net/twiki/bin/view/IVOA/InterOpOct2005VOQL/VOUnifiedQueryTalk.pdf =brian