Observational databases differ in both purpose and design. Each database is situated in different organizational settings and uses different terminologies or parameter denotations for describing their content (parameters/variables). Here, we aim to maximize reusability of MS registry/cohort data by harmonizing structure and variables by developing promoting the adoption of a “common data model”and developing a standardised data dictionary of commonly used MS data concepts.  A common data model (CDM) aims to achieve both syntactic* and semantic interoperability**. We built on top of the “OMOP CDM”. OMOP CDM is the common data model, originating from the Observational Medical Outcome Partnership (OMOP), which is now being implemented and updated by the OHDSI (Observational Health Data Sciences and Informatics) community.It is being used within the two large Innovative Medicine Initiative (European Medical Information Framework (EMIF)/European Health Data and Evidence Network (EHDEN))) projects which are the models for the MSDA infrastructure. The maturity, the scalability of and the community behind the OMOP CDM makes it the perfect candidate for the CDM. We aim to facilitate and support the local mapping by data sources to this CDM.

*Syntactic interoperability represents a common, agreed upon data structure. -> Grammar

**Semantic interoperability represents the common understanding of the syntactic interoperable data structure. -> Vocabulary

The following opportunities of the SwitchBox are formulated: