http://www.jslab.dk/articles/non.recursive.preorder.traversal.part3

http://www.perlmonks.org/?node_id=600456

http://arachnode.net/blogs/programming_challenges/archive/2009/09/25/recursive-tree-traversal-orders.aspx

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

http://news.php.net/php.db/41369