To make searching for it easier, here are the terms usually associated
with each technique:

>1) Interval method: using a low - high interval on each node such that
>all childrens' intervals are subsets of the parent's interval.

Nested Set

>2) Tree-code annotation: as a tree-code attribute (e.g., "1.2.3.4.5")
>such that you can find all children of "1.2.3" using the predicate
>treeCode LIKE "1.2.3.%".

Materialized Path

Typically the weakness of a missing explosion operation in SQL is
misused by object database vendors to sell their wares. My blog entry
about this issue:
http://blog.hibernate.org/cgi-bin/blosxom.cgi/2004/12/04#gettricked