XPath queries on streaming data

We present the design and implementation of the XSQ system for querying streaming XML data using XPath 1.0. Using a clean design based on a hierarchical arrangement of pushdown transducers augmented with buffers, XSQ supports features such as multiple predicates, closures, and aggregation. XSQ not only provides high throughput, but is also memory efficient: It buffers only data that must be buffered by any streaming XPath processor. We also present an empirical study of the performance characteristics of XPath features, as embodied by XSQ and several other systems.