A federated search engine groups search results from information sources using attributes of the search results. In grouping the search results, a first set and a second set of attributes are extracted from content in each set of search results received using information source wrappers. The first set of attributes defines a main clustering strategy, and the second set of attributes defines a sub-clustering strategy. A main grouping of the sets of search results received from the information sources is generated using the first set of attributes. The main grouping of search results includes a plurality of labeled groups with a plurality of search results in each group. A sub-grouping of search results is generated for each labeled group of search results in the main grouping of search results using the second set of attributes.