The other week I registered to attend php|works 2007, a PHP developer's conference put on by php|architect.

Back when I was in college, one of my employers had me work on a scheduling application. Basically, I helped make a PHP-based application which allowed managers to schedule their students at anytime of day or week.

At one point we had devised that an entire working block would be one entry in the database with a timestamp representing the start and end times of a block. We needed a way to pull all data for a given day.