I worked on a multi-tenant application with distinct trees present in one table and with one tree per table and so on. Fun fun fun!
But I've never had to use it, so I am just guessing.
Same article, different site: https://communities.bmc.com/docs/DOC-9902
And a paper: http://www.sigmod.org/publications/sigmod-record/0506/p47-ar...
Here's a comparison of the different approaches in a matrix: http://vadimtropashko.wordpress.com/2008/08/09/one-more-nest...
I experimented with a variation by Vadim Tropashko using something called "Farey fractions" [1]. These represent the intervals as a 2x2 matrix of four integers rather than two floating point values.
The numbers are effectively limited to 32-bit values in the matrix since a multiplication is required (resulting in 64-bit intermediate results).
It was very interesting, but couldn't model a file system hierarchy well. It could roughly 10^32 items in the best case, but a very small number (hundreds) in edge cases.
For example, it maxes out at a depth of 17 with 100 items at each level, or a depth of 34 with 10 items each. This might be fine for modeling some hierarchies, but definitely not a file system. The edge case is if the fraction extends along one edge. So if we have 10 items per level, and add a child at the leftmost edge each time, we create the most costly fractional subdivision. Do this 35 times and you hit an math overflow.
[1] Check out the Chapter 5 and Errata links: http://vadimtropashko.wordpress.com/“sql-design-patterns”-bo...