DDI and Scientific Knowledge Graphs Interoperability Framework - CESSDA's Plans and work so far in the OSTrails Project

Interoperability of metadata across research infrastructures remains a major challenge for advancing Open Science. Aligning domain-specific standards with domain-agnostic frameworks is crucial for enabling cross-disciplinary discovery and FAIR data reuse. The OSTrails project addresses this by developing the Scientific Knowledge Graphs Interoperability Framework (SKG-IF) - a core model and set of API endpoints for metadata harmonisation. As part of its contribution, CESSDA has mapped its metadata standard, DDI Codebook 2.5, to SKG-IF. This mapping supports exposing CESSDA metadata via SKG-IF endpoints, enabling broader interoperability across systems. API development will continue in 2026, so the current endpoints are preliminary. As a Horizon Europe initiative supporting EOSC, OSTrails contributes to building open, reusable, and interoperable data infrastructures. CESSDA’s work helps make social science data more FAIR and integrated into the wider EOSC ecosystem. This presentation will showcase CESSDA’s contributions to OSTrails, with a focus on the DDI-to-SKG-IF mapping, current API work, and FAIR benchmarking activities. The latter involved defining community-specific FAIR tests, evaluating digital objects, and providing feedback to improve FAIRness - demonstrating a practical path toward greater interoperability and quality in research data.