This module provides methods for working with nested set trees.  The
nested tree model is a way of representing hierarchical information in
a database.  This takes a different approach to the Adjacency List
implementation.  (see DBIx::Class::Tree::AdjacencyList which uses
parent relationships in a recursive manner).

WWW: http://search.cpan.org/dist/DBIx-Class-Tree-NestedSet/