Extensions - general discussion

[niquola]

[johngrimes]

One way to do this within a columnar structure is to have a field ID against each element, and an array of extension structures within each table that each refer to a field ID.

This gets messy if you take it all the way to primitive elements, which can technically be extended. We stopped short of supporting this, as we have yet to find anybody with a use for it. But it is still better than having an array of extension structs for every single element.

[johngrimes]

Another complication with representing extensions within a fixed schema is that they contain an "any" type (which can be found in some other places within FHIR also).

This requires a huge amount of fields to accommodate completely.

We ended up making the list of types that are encoded configurable (along with maximum nesting level), so that users could fit the schema to their data and achieve optimal performance.