I'm in the process of creating some new surveys in Survey 123 and I wanted to get a better understanding of how repeat tables are related to the survey feature service. If needed, I can create the feature service, repeat tables and relationship classes in Pro for use in Survey 123 but that might not be necessary depending on Survey 123s defaults.
By default do Survey 123 created repeat tables have simple or composite relationships class connections to their parent feature services?
Is there anyway to change that relationship class of those Survey 123 sourced items from simple to composite or vice versa in Portal or AGOL once a survey is published?
If so, will existing record update accordingly? For example, if the default is simple and it's changed to composite, would the change remove any related table records whose parent feature service record was deleted before the change?
By default feature services created by Survey123 will use a composite relationship. Survey123 can work with both simple and composite relationship types the main thing that Survey123 requires is a GlobalID to GUID & 1:M relationship.
If you would like to switch it to a simple relationship, unfortunately there isn't a way to do it directly in your organization. You would need to download the data as a file geodatabase and in ArcGIS Pro delete and recreate the relationship class using the other relationship type.
Since the relationship will be Global ID to GUID as long as the parent global ID and the value in the table for the parent global ID don't change, which deleting the relationship class and recreating it wont change global ID's. When the new relationship class is created the related records will be maintained.