A guest comment by Jens Klump, CSIRO Australia: The first DOIs for data were minted about ten years ago in the context of the project "Publication and Citation of Primary Research Data (STD-DOI)", which was funded by the German Research Foundation DFG. The original study on the feasibility of using DOI for the publication of research data, written in 1998, has now been released by the German Research Centre for Geosciences (GFZ) where the study had been conducted. The study was initiated by Joachim Waechter, head of the Centre of Geoinformation Technology at GFZ, and conducted as part of the degree programme for information specialists at Potsdam University of Applied Sciences (FH Potsdam). The aim of the study was to assess whether this new tool, Digital Object Identifier, could be used for data publication. The original version of the study is now incorporated into the collection of the GFZ Library. To my knowledge it is the earliest mention of using DOI for data.