Semantic Layer in Health Care: The Art of Riding a Bicycle (Preprint)

UNSTRUCTURED Health data interoperability is the central hill climb in contemporary digital health. Hospitals often accumulate data like mismatched spare parts, catalogued inconsistently, and difficult to re-use across care. The landscape of non-annotated source systems, legacy data warehouses that lack interoperable data models, the coexistence of multiple terminologies with divergent scopes, the operational turbulence of system migrations, and the persistent challenges of metadata catalogues and versioning set a starting point to a journey in building a semantic layer that makes data Findable, Accessible, Interoperable, and Reusable (FAIR), and that remains robust as terminologies evolve. Terminology updates are complex and their terms, classifications, and regulations continually change. This viewpoint article gives an exemplary historical overview at a Swiss university hospital, highlights the relevance of key decisions and projects and contrasts local conditions with the Swiss and European context. It notes perspectives of large clinical information systems and highlights organizational implications, tools and models needed, and the challenge of legacy data. It dives into project work of ontology creation. The discussion reflects on achievements and the future illustrating the cadence and resilience required to ride interoperable data “around the world”. Key Message. Achieving healthcare interoperability requires balancing diverse standards, terminologies, and data governance. The FAIR principles provide a framework. Organizational commitment to these practices is essential.