To cite the service as such, we suggest the following BibTeX entry:
@MISC{vo:GAVO_DC_IRK, year=2012, title={A Resolver for {IVOA} Identifers ({IVOID})}, author={The {GAVO} data center team}, url={http://gavo.aip.de/rr/q/nmah/info}, howpublished={{VO} resource provided by the {AIP} {DaCHS}} }