It's currently modeled as ORCL1|PDB1|db_high.adb.oraclecloud.com

Service name (being the most broad?) should probably go first.

The db.namespace is also associated with connection and is usually retrieved from connection string, and it's not clear if all three things can be specified there. It seems connection string would include service_name, instance id, or both of them, while the database name is an internal name not visible to the client.