http://www.jslab.dk/articles/non.recursive.preorder.traversal.part3
http://www.perlmonks.org/?node_id=600456
http://www.google.co.jp/search?hl=ja&safe=active&client=firefox-a&hs=ZSZ&rls=org.mozilla:ja:official&q=preorder traversal php json&aq=f&aqi=&aql=&oq=&gs_rfai=
http://safalra.com/programming/php/directory-tree-traversal/
http://articles.sitepoint.com/article/hierarchical-data-database/2
http://dev.mysql.com/tech-resources/articles/hierarchical-data.html
http://bakery.cakephp.org/articles/view/modified-preorder-tree-traversal-component
http://www.zend.com/zend/tut/tutorial-ferrara2.php?article=tutorial-ferrara2&id=3453&open=1&anc=0&view=1
http://simon.incutio.com/archive/2003/06/19/storingTrees
http://istherelifeafter.com/joecelko.html
http://www.codeproject.com/cs/database/Trees_in_SQL_databases.asp
and here’s an ASP technique that looks interesting
http://www.4guysfromrolla.com/webtech/101202-1.shtml