During my work as an IT consultant I have also implemented systems for resource planing for many years (both objects and human resources). Based on this know-how I and my colleague have generated a generic data model for organigrams which is especially optimized for this purpose.
The basic idea is to introduce so called person groups which are linked together like recursive mailing lists. This enables both arbitrary hierarchical and composite-like structures of those groups.
Attached to the person groups are persons, disposable objects and event types. These entities are linked together by events. Users of the system are also authorized by attaching privileges to person groups like „write events for objects of department Logistic“, „write events for persons and event types of department OS Administration“.
I sketch this data model further on our blog apextipps: