снова про деревья / PostgreSQL : Форум на SQL.RU
http://www.sql.ru/forum/actualthread.aspx?tid=499910 simple tree for cascade menues in postgers
Tree
General trees persisted in relational databases - The Code Project - C# Database
http://www.codeproject.com/cs/database/persisting_trees.asp
Trees in SQL databases - The Code Project - C# Database
http://www.codeproject.com/cs/database/Trees_in_SQL_databases.asp how to create tree in sql database