Efforts to make sense of the number and diversity of scholarly publication channels started relatively early, mostly with a focus on journals. Already in the late 19
th century, the Royal Society of London listed scholarly journals, as distinct from professional journals, for the purpose of producing the
Catalogue of Scientific Papers published globally (
Csiszar, 2017). Research libraries have also had an increasing interest, from the point of view of collection management, to list and prioritize academic/scholarly journals (
Nisonger, 1988). The purpose of the first journal ranking produced in 1926 was to determine, based on citations, which chemistry journals were indispensable for a university library with scarce resources (
Gross & Gross, 1926). Ulrich’s Periodicals Directory, started in 1932, is the most elaborate library directory of over 300,000 serials, including peer-reviewed journals. The International Standard Serial Number (ISSN) has been used since 1975 to identify serial publications—including journals and series of books and proceedings — and issued globally to over 2,000,000 titles.