Résumé
The OntoPortal Alliance is a consortium of several research and infrastructure teams dedicated to promoting the development of ontology repositories ––in science and other disciplines–– based on the open, collaboratively developed OntoPortal open source software. Teams in the Alliance develop and maintain several openly accessible semantic artefact catalogues or ontology repositories in multiple disciplines. The list of repositories is available on the Alliance web page and the teams are listed on GitHub. The OntoPortal Alliance members and other partners gathered from Sept. 29 to October 3rd, 2025 in Berlin for the 4th OntoPortal Workshop. The meeting involved around 20 persons including management, research and technical profiles. The 2025 workshop’s main goals were to consolidate the OntoPortal Alliance organization and shared agenda, and to engage with newcomers. The program included several sessions (technical, content, management) as well as a newcomers session which featured four new use cases in social science, heritage science, cultural heritage, and astronomy.The workshop opened with presentations on OntoPortal, its federation, and the MOD-API, followed by discussions on SAC technologies and integration opportunities with TS4NFDI outcomes. Subsequent sessions explored federation strategies, governance, and collaboration perspectives, particularly in the context of EOSC. The second and third days focused on consolidation, new use cases, onboarding of emerging instances, and technical developments, including AI integration and metadata practices. The workshop concluded with developer discussions and a synthesis of priorities, reinforcing the shared vision of interoperable and FAIR semantic artefact infrastructures. The event demonstrated the clear motivation and commitment of the Alliance members to collaborate on the OntoPortal technology and the implementation of ontology-based services in general. This document is a summary of the discussions and the decisions taken.