WSDM is an audience driven design method for web sites. By explicitly starting from the requirements of the web sites audience (the users or visitors), WSDM avoids problems caused by poor underlying design, or by a too data or organization driven view. This paper presents how the main structure of a web site can be derived from structuring the visitors of the web site into one or more so-called Audience Class Hierarchies. Each Hierarchy represents a classification of the visitors according to one aspect. All Hierarchies have the same top, i.e. the class Visitor representing all potential visitors of the web site. Furthermore, the presented methodology forces its user to deeply reflect on the requirements of the visitors, and to resolve any semantic conflict at design time. This greatly enhances the correctness of the obtained Audience Classes. The given algorithm also allows for computer-aided support of WSDM.