1. A computer-implemented system for searching a database of item listings, said computer-implemented system comprising: a database component for storing said item listings, each of said item listings having associated attributes, the item listings each being categorized into at least one of a plurality of categories, at least one attribute being shared by item listings having mutually exclusive categories; and a database engine server, said database engine server receiving a set of requested attributes for a requested item in a requested category, said database engine server returning a set of item listings from said database component having said requested category and said set of requested attributes.