In light of the ongoing transformation of scholarly publishing toward open access, libraries need data-based tools that enable them to make decisions that respond to the challenges posed by this shift. Tasks such as collection development, applications for funding, or consulting researchers on publication venues require a solid base of data, which is not always easily available to librarians. Funded by the German Federal Ministry of Education and Research (BMBF), the Open Access Monitor Germany (OAM) aims to provide libraries, funders, and researchers with a freely available tool that presents data on publications and citations for analysis. The OAM records the publication output of German academic institutions in scientific journals. Through analyses of subscription fees and (open access) publication fees, it helps to monitor and support the transition of the publishing system toward an open access system. To this end, data from existing sources are collated within an expanded database, made available to users in an open interface, and disseminated by means of scientific publications. The OAM draws on sources such as Unpaywall, Dimensions, Web of Science, Scopus, and OpenAPC. Unpaywall is used as a central data source for publication metadata including open access availability; this data is then matched with Crossref data for journal-level metadata and finally with Dimensions, Web of Science and Scopus data for affiliations and citation data. The connection to OpenAPC provides data on publication costs for each participating institution. The interface https://open-access-monitor.de/publications presents users with a wide range of filters that can be used to customize the underlying data in line with specific needs. Users can switch between Dimensions, Web of Science and Scopus affiliations and make use of different analysis types including publication analyses, cost analyses, and citation analyses. Results are presented as tables as well as charts and can be downloaded for further use. In the future, additional data sources including subscriptions to scientific journals and subscription payments will be integrated to allow the shift in payment flows in the changing publication market to be observed. The integration of data from the electronic resource management system LAS:eR has already been initiated and will soon be completed. Moreover, interfaces will be created to connect the Alma and FOLIO systems. Together with data on publication costs, this will provide participating institutions with easily accessible overview of their total costs, thus enabling them to calculate an integrated budget for subscriptions and publications. Institutions using the OAM are advised with regard to analyzing data and technically integrating the OAM into their own applications. Small and medium-sized publishers from German-speaking countries are supported in the negotiation of transformation contracts by means of data from the OAM. The OAM project team also conducts studies that address a number of scientific issues, for example the impact of open access on scientific networks and the role of open access in the field of monographs. The relationship between open access and the citation rates of published works is another possible research area that can be addressed with the help of the OAM.

The transition process from the subscription model to the open access model in the world of scholarly publishing brings a variety of challenges to libraries. Within this evolving landscape, the present article takes a focus on budget control for both subscription and publication expenditure with the opportunity to enable the shift from one to the other. To reach informed decisions with a solid base of data to be used in negotiations with publishers, the diverse already-existing systems for managing publications costs and for managing journal subscriptions have to be adapted to allow comprehensive reporting on publication expenditure and subscription expenditure. In the case presented here, two separate systems are described and the establishment of joint reporting covering both these systems is introduced. Some of the results of joint reporting are presented as an example of how such a comprehensive monitoring can support management decisions and negotiations. On a larger scale, the establishment of the National Open Access Monitor in Germany is introduced, bringing together a diverse range of data from several already-existing systems, including, among others, holdings information, usage data, and data on publication fees. This system will enable libraries to access all relevant data with a single user interface.