FHIR Chat · Optional slices and goFSH

Stream: shorthand

Topic: Optional slices and goFSH

Morten Ernebjerg (Jun 07 2021 at 10:41):

Hi :wave: I'm using goFSH tool to turn an existing Composition profile designed in Forge into FSH. The profile slices Composition.section and one of those slices is optional (0..*, to be precise). The corresponding entry in the StructureDefinition has neither min nor max fields:

{
    "id": "Composition.section:questionnaire",
    "path": "Composition.section",
    "sliceName": "questionnaire",
    "short": "Questionnaires used in the software"
}

In addition, two fields in the entry element are defined as required in that slice. However, running goFSH on this gives a required slice in FSH:

* section contains
    [other slices]
    questionnaire 1..* and
    [other slices]

which indeed compiles into an a slice entry like the above, except that it explicitly sets min and max to 1 and *, respectively. So it seems goFSH assumes that the default minimum slice cardinality is 1. I didn't see any statement on this (or the contrary) in the ElementDefinition documentation - was this a deliberate choice?

Chris Moesel (Jun 07 2021 at 13:14):

I don't think that is a deliberate choice. It may be a bug. Is there a public FHIR JSON/XML representation we can look at to try to reproduce this?

Morten Ernebjerg (Jun 07 2021 at 16:02):

Hi @Chris Moesel, here is a minimal example that leads to this behavior - the quest slice should be optional but gets converted into a required slice.

Composition-prof.StructureDefinition.json

I discovered that this is related to the fact that the profile also sets the cardinality of Composition.section to 1..*. If that cardinality is set to 0..*, the slice remains optional (is set to 0..*). However, since the slicing is open, it is of course valid to only have an optional slice.

Chris Moesel (Jun 07 2021 at 17:04):

Thanks... we're a bit tied up at the moment trying to get some last minute things in for FHIR DevDays, but hopefully we can take a look at this soon. Your example and analysis is very helpful. Thank you!

Morten Ernebjerg (Jun 07 2021 at 18:02):

A worthy cause - after all, I myself learned FSH from your session at the last DevDays :nerd:

Chris Moesel (Jun 16 2021 at 22:17):

I've logged this as GoFSH#135. We hope to fix this in the next two-week sprint (which starts tomorrow).

Last updated: Apr 12 2022 at 19:14 UTC

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FHIR Chat · Optional slices and goFSH · shorthand