Peng, FengChawathe, Sudarshan S.We have implemented and released the XSQ system for evaluating XPath queries on streaming XML data. XSQ supports XPath features such as multiple predicates, closures, and aggregation, which pose interesting challenges for streaming evaluation. Our implementation is based on using a hierarchical arrangement of pushdown transducers augmented with buffers. A notable feature of XSQ is that it buffers data for only as long as it must be buffered by any streaming XPath query engine. We present a detailed experimental study that characterizes the performance of XSQ and related systems, and illustrates the performance implications of XPath features such as closures. (UMIACS-TR-2003-62)en-USTechnical Report