Simple Introduction to the WITH clause in SQL99 http://www.teradata.com/tdmo/v06n03/Tech2Tech/InsidersWarehouse/OddballSQLTricks.aspx
For a comparison of Oracles "CONNECT BY" with SQL99 WITH look here http://gppl.moonbone.ru/
a patch for postgresql to implement SQL99 (up to 8.2) is here http://gppl.moonbone.ru/
look a ltree: http://www.sai.msu.su/~megera/postgres/gist/ltree/
look at: http://people.planetpostgresql.org/merlin/index.php?/archives/2-Dealing-With-Recursive-Sets-With-PLPGSQL.html
