A virtual directory server (VDS) processes requests based on a first hierarchical model while using a backend server operating based on a relational model. In one embodiment, classes representing the tables and columns in the relation model are generated according to a second hierarchical model (class hierarchy). On receiving a directory request for values' corresponding to attributes in the first hierarchical model, tables and columns corresponding to the requested attributes are identified. A query according to the relational model is constructed employing the generated classes (of the second hierarchical model), the query including the identified tables and columns. The query is then executed in the backend server to retrieve the values corresponding to the attributes, and the values are then sent (according to the first hierarchical model) as a reply to the directory request.