Related axis: the extension to XPath towards effective XML search

We investigate the limitations of existing XML search methods and propose a new semantics, related relation- ship, to e®ectively capture meaningful relationships of data elements from XML data in the absence of structural constraints. Then we make an extension to XPath by introducing a new axis, related axis, to specify the related relationship between query nodes so as to enhance the °exibility of XPath. We propose to reduce the cost of computing the related relationship by a new schema summary that summarizes the related relationship from the original schema without any loss. Based on this schema summary, we introduce two indices to improve the performance of query processing. Our algorithm shows that the evaluation of most queries can be equivalently transformed into just a few selection and value join operations, thus avoids the costly structural join operations. The experimental results show that our method is e®ective and e±cient in terms of comparing the e®ectiveness of the related relationship with existing keyword search semantics and comparing the e±ciency of our evaluation methods with existing query engines.