Efficient evaluation of linear path expressions on large-scale heterogeneous XML documents using information retrieval techniques

We propose XIR-Linear, a method for efficiently evaluating linear path expressions (LPEs) on large-scale heterogeneous XML documents using information retrieval (IR) techniques. LPEs are the primary form of XPath queries, and their evaluation techniques have been researched actively. XPath queries in their general form are partial match queries, and these queries are particularly useful for searching documents of heterogeneous schemas. Thus, XIR-Linear is geared for partial match queries expressed as LPEs. XIR-Linear has its basis on existing methods using relational tables (e.g., XRel, XParent), and drastically improves their efficiency using the inverted index technique. Specifically, it indexes the labels in label paths (i.e., sequences of node labels) like keywords in texts, and finds the label paths matching the LPE far more efficiently than string match used in the existing methods. We demonstrate the efficiency of XIR-Linear by comparing it with XRel and XParent using XML documents crawled from the Internet. The results show that XIR-Linear outperforms XRel and XParent by an order of magnitude with the performance gap widening as database size grows.