Hi Tim,

Thanks for that link to Joe Celko's article, I had not come across this solution before. I can see that it is easier to model an org tree in SQL using set theory. In practice, does the data in the set correspond to an organisation's departmental structure, rather than individual relationships, otherwise you could get real problems if an employee switches managers and correspondingly needed to switch containments?

I like the idea that because the containment encapsulates all levels of the hierarchy, there is no break in the management chain if an employee in the middle-tier leaves, the model is effectively self-healing.

Presumably by creating overlapping sets you could also create organisation structures where individuals have multiple lines of management (many DBAs may be familiar with this    )

David