Keeping track History Maintainance--Design Issue

Hi all,
i do have a new module named as Project Costing, in which i
have to create a Heirarchy of Activities,
Some thing of this sort
Project
|--Phase1
|--Stage1
|--Phase2
|--Stage2
This can go at any level, but In each stage i need to have to add
cost categories involved, which again constitutes to another eight
Tables excluding the top oNe which can be built with Two tables.
Problem
When ever i define a project it comes into an estimate Mode.
Then there is a seperate link For project update, I should not touch
what i have done in Project Estimate, because i need to compare what i
have done in Estimate and actuals,
do i have to replicate the same tables[ might involve atleast 10
tables] and do it or do i have to manage with the same table.
I can give you any sort of input for this
Thanks in advance
thomsonIf the hierarchy can have a fixed number of levels, consider designing a
regular relational model - physically with as many tables as there are level
s.
However, if your requirements suggest variable levels of hiearchy, consider
using a tree/hierarchy model. Google for "trees and hieararchies" or search
this news group for more info.
But rememer - an efficient hierarchy is based on a physical model that
prevents circular referencing. Which can be a b*tch. ;)
In both of the above models you have the option of storing multiple node
properties separately - e.g. costs, estimates, etc.
ML