Here's a link to an article that discusses a relatively simple way of handling trees in SQL tables. It's called "the adjacency model".

http://sqllessons.com/categories.html

Using unions to retrieve entries in a fixed number of sub-categories:

http://forums.mysql.com/read.php?97,167556,167556

There is an alternate algorithm which is more involved to implement but is much faster called "the nested set" model:

http://articles.sitepoint.com/article/hierarchical-data-database/2

Another article on the nested set algorithm:

http://dev.mysql.com/tech-resources/articles/hierarchical-data.html

As reported on slashdot:

"The San Francisco Chronicle reports that Google has released Jarlsberg, a 'small, cheesy' web application specifically designed to be full of bugs and security flaws as a security tutorial for coders, and encourages programmers to try their hands at exploiting weaknesses in Jarlsberg as a way of teaching them how to avoid similar vulnerabilities in their own code. Jarlsberg has multiple security bugs ranging from cross-site scripting and cross-site request forgery, to information disclosure, denial of service, and remote code execution. The codelab is organized by types of vulnerabilities."

As more and more friends of mine move over to government work, I was reminded of the 7 phases of a government project:

1. Exultation

2. Disenchantment

3. Confusion

4. Search for the guilty

5. Punishment of the innocent

6. Accolades for the uninvolved

Enjoy. ;)

http://www.startupnation.com/community/

http://econnect.entrepreneur.com/