Ubercart is the most popular e-commerce software for the Drupal Content Management System.  It uses attributes for specifying variations for a product.  Attributes can specify color or size of a article of clothing or they can specify different sizes of a product, each with their own price and SKU. 

Often the possible selection of choices for one attribute may depend on the choice of another attribute.  For example, the available color of a shirt may depend on the size selected.  The uc_dropdown_attributes module allows an attribute to be displayed depending upon the choice selected for another attribute.  So the medium colors attribute will be displayed when the medium size is chosen. If the small size is chosen then the small colors attribute will be displayed.  Each colors attribute contains only the colors that are available in that size. 

The uc_dropdown_attributes module presents an administrative interface for defining the relationships between attributes and which choice of an attribute will trigger the display of another attribute under the Dependencies tab in the edit tab.  An example of the implementation of the uc_dropdown_attributes module can be seen at http://dropdown.gaiaes.com/node/3.

The Drupal.org sandbox page is at http://drupal.org/sandbox/trobey/1162770.

Download: uc_dropdown_attributes