Hi Dieter, thanks for your suggestion. After a little bit of work, finally I got it. Now seems that my product works and doesn't have those assertion problems mentioned by Chris. Here is the product page if somebody has a feedback: http://zope.org/Members/jmeile/JMBoring Greetings, Josef

Make them additional constructors in your "registerClass". This ensures that they are registered in your "Product factory" and can be accessed in the usual way.