You should not put multiple ACI IDs into an Author attribute. Instead, expose the Author key in each ACI record when you design your API message definition. This way, the data warehouse team can treat Author and ACI as separate entities and join them by key. simiply
Keep the primary key of each entity within that entity.
Use associations to link them, not attributes holding multiple IDs.
Correct design pattern
Author entity
Attributes: AuthorID (primary key), Name, etc.
Association: 1‑* to ACI
AuthorCitationIndex entity
Attributes: ACIID (primary key), CitationCount, Year, etc.
Association: *‑1 to Author (store AuthorID as foreign key in the API mapping)
Sample
{ "AuthorID": "2000", "Name": "Guru", "ACIs": [ { "ACIID": "456", "CitationCount": 20, "Year": 2022, "AuthorID": "123" }, { "ACIID": "789", "CitationCount": 15, "Year": 2023, "AuthorID": "123" } ]}
I hope this helps you