Fast SLCA and ELCA computation for XML keyword queries based on set intersection

In this paper, we focus on efficient keyword query processing for XML data based on SLCA and ELCA semantics. We propose for each keyword a novel form of inverted list, which includes IDs of nodes that directly or indirectly contain the keyword. We propose a family of efficient algorithms that are based on the set intersection operation for both semantics. We show that the problem of SLCA/ELCA computation becomes finding a set of nodes that appear in all involved inverted lists and satisfy certain conditions. We also propose several optimization techniques to further improve the query processing performance. We have conducted extensive experiments with many alternative methods. The results demonstrate that our proposed methods outperform existing ones by up to two orders of magnitude in many cases.