To cite the service as such, we suggest the following BibTeX entry:
@MISC{vo:purx_OAI_PMH, year=2017, title={purx Publishing Registry Proxy}, author={Demleitner, M.}, url={http://dc.zah.uni-heidelberg.de/purx/q/pmh/info}, howpublished={{VO} resource provided by the {GAVO} Data Center} }