A method of facilitating location of a data item describing, for example, a product or service that is the subject of on-line auction, commences with the presentation of a category navigation interface. The category navigation interface allows a user to navigate a "virtual" hierarchy of categories and to select a target virtual category of the virtual hierarchy. The target virtual category is then identified as being linked to an actual category, within an actual hierarchy of categories. Database items are classified only in terms of the real hierarchy of categories, and not the virtual hierarchy of categories. Having then identified an actual category to which the virtual category is mapped, data items of the real category are identified responsive to the user selection of the virtual category of the virtual hierarchy of categories.