To cite the service as such, we suggest the following BibTeX entry:
@MISC{vo:GCP_Reg, year=2008, title={{PVOL} {EPN}-{TAP} Registry}, author={Planetary Sciences Group, {UPV}/{EHU}}, url={http://pvol2.ehu.eus:8083/__system__/services/registry/info}, howpublished={{VO} resource provided by the {PVOL} {EPN}-{TAP}} }