shopping cart classes

I've checked out the shopping cart packages available for PHP and am not thrilled by any of them. Was wondering if there are a set of classes available that could be used to support a shopping cart. I'm interested in the 'back end' -- working with the actual data, rather than the front end -- the user interface. Want to build it with php + mySQL or PostgreSQL. I want complete freedom to build the interface but don't want to reinvent the wheel for credit card validation, online credit card processing, shipping calculation, etc. I've built a simple shopping cart for a site currently under construction. This uses a combination of javascript and php, and doesn't use database (less than 1 dozen items). You can see an example (excuse the mess) by going to: http://www.bhagavati.com/trial/mainframe.htm and clicking the 'order' link in the navbar frame at the top. HINT: close movie window as soon as it opens. Randy Perry sysTame Mac Consulting/Sales