Semantic Query Optimization for XQuery over XML Streams

We study XML stream-specific schema-based optimization. We assume a widely-adopted automata-based execution model for XQuery evaluation. Criteria are established regard-ing what schema constraints are useful to a particular query. How to apply multiple opti-mization techniques on an XQuery is then ad-dressed. Finally we present how to correctly and efficiently execute a plan enhanced with our SQO techniques. Our experimentation on both real and synthetic data illustrates that these techniques bring significant performance improvement with little overhead.