Work, expression, manifestation, item, one, two, three, four,… a heady nursery rhyme that people working in libraries are now familiar with. Indeed, these four concepts are regularly chanted in specialised conferences and in library science classes. More broadly, they reflect an evolution of bibliographic models (LRM), cataloguing rules (RDA) and data exchange formats (Bibframe). Our French neighbours usually call this movement the “bibliographic transition”. And the rero ils project does not escape it, quite the contrary: it is fully imbued with it. The use of Bibliostratus shows this.