Working on the french national building registry. We record every single building in the country, attach a unique number and distribute this number in many databases (public and private) as a pivot key. The goal is to create new analysis using data spread in different databases. Since nobody has a perfect database and no algo can detect everything, we are opening the database so any public structure, private company and citizen can participate to the content (think OpenStreetMap for an official state database). The url : https://rnb.beta.gouv.fr (in french)