Publication services and research information systems are indexed in various directories (e.g. OpenDOAR, re3data, FAIRSharing, DOAJ, DRIS), sometimes in parallel. Furthermore, aggregators and citation databases (e.g. BASE, OpenAIRE, DataCite) use them for the purpose of indexing their content or for assigning PIDs. This results in multiple identifiers being assigned to the same services and systems, and they often operate under different names. This can lead to duplicate registrations of the same sources, especially for aggregators and providers of value-added services, and can require time-consuming mapping. In the planned project, the aim is to examine which PID systems are suitable for addressing OA publication services and research information systems or similar services. So far, only a few initiatives, such as re3data and FAIRsharing, assign DOIs for research data repositories.