The first EOSC catalogue hackathon proved federation could work. The second made it more real: messier, broader, and much more useful. With EOSC Beyond, Data Terra, ENVRI, EMBRC, EGI, GRNET, and the Life Science Connect node in the room, we moved from “can catalogues talk?” to the harder question: “can they understand each other well enough to build on?”

There is a reasonable argument that the best way to design an interoperability standard for EOSC service catalogues is to look at what nodes are actually publishing before deciding what to mandate. So I pulled 239 service records from the EOSC Beyond sandbox, compared them against the EEN specification and a draft EEN-to-DCAT field mapping being developed within the working group, and mapped the results across all three schemas. The short version: the divergence between the two formats in active production use is real, it is already in the wild, and the empirical common core is smaller than either spec requires. Which is, somewhat inconveniently, the strongest possible argument for starting there.