Automaton Meets Query Algebra: Towards A Unified Model for XQuery Evaluation over XML Data Streams Jinhui Jian, Hong Su, and Elke A. Rundensteiner   View Paper (PDF)   Return to Views and XQuery Approaches Abstract In this work, we address the efficient evaluation of XQuery expressions over continuous XML data streams, which is essential for a broad range of applications including monitoring systems and information dissemination systems. While previous work has shown that automata theory is suited for on-the-fly pattern retrieval over XML data streams, we find that automata-based approaches suffer from being not as flexibly optimizable as algebraic query systems. In fact, they enforce a rigid data-driven paradigm of execution. We thus now propose a unified query model to augment automata-style processing with algebra-based query optimization techniques. The proposed model has been successfully applied in the Raindrop stream processing system. Our experimental study confirms considerable performance gains with both established optimization techniques and our novel query rewrite rules. ©2005 Association for Computing Machinery