I imagine that when I upload a file as a complex obs, I'd like to also give a description for the file, so that it can be displayed prettily on the patient dashboard.

There's no easy way to do this with the proposed data model here, besides having an obs group that contains the complex obs and also a free-text obs. Which doesn't sound right.

To follow the HL7 lead (again)¹...

HL7 defines the following model:

• concept_complex
  • source: "a unique name that identifies the system that is the source of the data." For us, this would be a reference to the handler ... perhaps it could be a FK to a concept_complex_handler table?
  • type: mime type²
  • subtype : mime sub type²
  • encoding : A = ASCII, Hex = hex digits, or Base64³

So, we'd need the concept_complex table modeled and the concept editing screens adjusted so that setting the datatype to complex would open the fields for the complex type specifics.

Then add the obs.value_complex as a text attribute (we need to decide on length for this field...probably should err on bigger...but not too big to bloat obs table). This would contain the URN information that comprises handler + unique key for handler to find resource. Etc, etc. as you've described.

RE: darius' comment about including support for a "title" ... well, we should discuss it and bring a solution back here.

¹ HL7 2.6 2.A.24
² RFC 2045
³ Base64 on Wikipedia