require that the value going into a Coding's system slot is a URL

[turbomam]

No description provided.

[gaurav]

Yeah, it does seem strange to me that https://cancerdhc.github.io/ccdhmodel/v1.1/coding__system/ is a string rather than a URI.

@bfurner @mbrush Is there a reason for this?

[bfurner]

i believe this was left as string since at the time we didn't have strong recommendations for how reference data like code systems should best be encoded in the model. FHIR has this as a very permissive uri type (Regex: \S*) that can be further constrained. one could obviously further constrain this to a resolvable url, but there are some source systems that may not have resolvable urls for their code systems (e.g. GDC, PDC, etc.) and when we try to encode the "original" values from the source in a Coding, we may need to accept that there are non-resolvable urls at least in the short term.