It looks like some tables are missing in the ERD. For example campaign_customer_group table contains campaign_id and customer_group_Id. Campaign_id can be looked up in the Campaign tables but there is no table to lookup customer_group_id and all the customers that are part of that group.  Source_code_group_id from the Campaign_source_code_group has the same issue of missing a table with the details about it.

Here are some links to documentation on Customer Groups and Source Code Groups

example of SFCC import/export of CustomerGroups

https://developer.salesforce.com/docs/commerce/commerce-api/references/source-code-groups?meta=getSourceCodeGroup