What is the best way to store user generated conditions and consistently check them?

Question

An application keeps track of hundreds of variables. Users are able to create conditions which can be simple (ex: if one variable is true) or complex (ex: if 34 variables are true AND 22 variables are false AND 2 variables are equal to each other). If the condition ever becomes true, it fires off some action. What is the best way to achieve this?

Answer 1

What you are looking for in general is a business rules engine (BRE). There are lots of lightweight and more heavy BREs out there. Depending on your specific needs, you should be able to find one that fits your requirements.

Answer 2

The post by JP on BREs seems to be the way to go. Drupal CMS is implementing a Rules engine, http://drupal.org/project/rules http://groups.drupal.org/node/10270

It may help with your situation since you need a solution in PHP.