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how much of upper is actually enforced at runtime vs just used for schema generation? like if a downstream system silently breaks a semantic assumption (say, infers enum incorrectly or drops a type constraint), does uda catch that anywhere or is this trust-based across projections?

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Great question. It really depends on the projection. For example, the projections to GraphQL and Java are mostly limited to what can be expressed there. But the projection to SHACL has access to all of SPARQL Constraints, which is what's used for the bootstrapping knowledge graph. We are looking into being able to do more runtime validation for data in the warehouse.

got it, thanks. makes sense that it depends on the projection target. SHACL+SPARQL seems like the strongest runtime check layer then. for projections like graphql or java where enforcement is weaker, is there any way to inject runtime guards or contract tests as part of the generated code? or is the idea to keep enforcement external and just let uda define the schema canonically?

We have a little bit of runtime checks in the Java projections but it's still tied to SHACL/SPARQL through the Jena library. We are exploring ways to keep using SHACL at scale for advanced data profiling, and also try to identify a subset of SHACL constraints which would be able to compile down to SQL constraints for validating directly against the data warehouse.

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