Attribute ExternalID on occurrence

When we create object, models and occurrences based on the data of external systems, we miss a possibility to set a free text identification also on Object or Connection Occurrence. Therefore we are not able to identify afterwards, if the occurrences were created manually or by a report from external data.

There is already an External GUID possible to be set, but normally we do not have GUID format, but another sort of identification (alphanumerical). We need an equivalent, but as a free text, with the proper methods (e.g. attribute External ID, methods in report setExternalID, getExternalID). It would be better to have it on Occ class, instead of ObjOcc.