Generating Improved Document Classification Data Using Historical Search Results

A server system accesses, respectively, historical query information for queries that have search results corresponding to first information items and second information items and classification data of the first information items. Initially, the first information items are classified and the second information items are unclassified. Based on the classification data of the first information items and the historical query information, the server system generates classification data for the second information items and stores the generated classification data therein. In response to requests for service from client devices, the server system provides customized services to the client devices using the second information items and the corresponding classification data generated for the second information items.