A configurator using structure and rules to provide a user interface. According to one embodiment of the invention, a customizable product class is created. The customizable product class includes a set of one or more attributes to define the customizable product class. A component product class is added to the customizable product class, where the component product class is a subclass of the customizable product. A customizable class rule is associated to the customizable product class, the customizable class rule including expressions which provide conditions on component products added to the customizable product. A customizable UI is mapped to the customizable product class, where the customizable UI provides access structure to the configurator.