title: the xxl search engine : ranked retrieval of xml data using indexes and ontologies. authors: a theobald , g weikum. venue: sigmod conference. year: 2002
title: the compass search engine for unified ranked retrieval of heterogenous xml and web data. authors: j graupmann , m biwer , c zimmer , c zimmer , m bender. venue: proceedings of the 30th vldb conference , toronto , canada ,. year: nan