Hi Mike,

found a further article at http://www.intelligententerprise.com/001020/celko1_1.jhtml

It appears that if your organisation structure fequently changes, you would still need an adjacency list to calculate the nested sets though? Joe provides the code to convert one to the other. I guess the practical application of this solution  would be to write a trigger which recalculates the nested sets whenever the organisation structure is changed (i.e. you change an employee's manager id), storing the left and right values you calculate and using them as an aid to produce faster organisation structure reports.

If someone left the organisation, you would leave the existing calculated left and right values in place to provide a management hierarchy until a new manager was appointed.

PS: Have had several coffees now

David