Efficient XML Query Processing in Mediators

With the advent of XML as the standard for data representation and exchange over Internet, there are ever increasing applications, E-Commerce application in particular, using XML as a mediator model. It raises the issue on how to evaluate XML queries efficiently in mediator systems. In this article, we address the problem of multiple query optimization in a XML based mediator. Because the XML query language differs from SQL/OQL in its pattern matching and regular path expression constructs, the way of identifying common subexpressions of multiple XML queries is different accordingly. We present the steps to identify common subexpressions. To obtain the global query plan, we propose some heuristics to reduce the whole search space. By using statistic method to estimate the usage frequency of the common subexpressions in XML queries,a selective caching and materializing of remote data can be accurately made,this will greately improve query response time.