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An XML-algebra for efficient set-at-a-time execution

The importance of XML query optimization is growing due to the rising number 
 of XML-intensive data mining tasks. Earlier work on algebras for XML query 
 focused mostly on rule-based optimization and used node-at-a-time execution 
 model. Heavy query workloads in modern applications require cost-based 
 optimization which is naturally supported by the set-at-a-time execution 
 model. This paper introduces an algebra with only set-at-a-time operations, 
 and discusses expression reduction methods and lazy evaluation techniques 
 based on the algebra. Our experiments demonstrate that, for queries with 
 complex conditional and quantified expressions, the proposed algebra results 
 in plans with much better performance than those produced by the 
 state-of-the-art algebras. For relatively simple queries, the proposed 
 methods are expected to yield plans with comparable performance.