In any case, as long as your structures satisfy:
- no node can have more than (say) 4 million children
- the structure may not be deeper than (say) 100 levels this representation may suit your needs better than the one from 'SQL for Smarties': it is as fast as that one on lookup, much faster on insert and delete.
If you want to take a look at a (very) preliminary description I started writing back in may, download the preliminary paper and coding function .
Do not hesitate to contact me if you are interested in the stuff and think I may help implementing it.