Cooperative Evaluation of XML Queries in Mediators

Abstract

As XML becomes the de facto standard for data representation and exchange over Internet, there are ever increasing applica tions using XML as a middleware model. Network-computing paradigm is also changing; it shifts to mobile agent paradigm. Building a mediated query system by combining both XML and mobile agent technologies is very promising.

In this paper, we address the problem of cooperative evaluation of XML queries by exploiting mobile agent technologies. Our contribu tions are as follows: By introducing a new operator—the variable binding operator, we represent XML queries' pattern body as a special operator tree, and an evaluation method of the variable binding operator is presented to match the XML queries' pattern body with the XML data graph by exploiting automaton theory. In the case of XML data involving XML-Link, by introducing a proxy operator, a novel al gorithm is given to evaluate the XML queries cooperatively, that is, by representing the subquery operator tree with XML, it can be sent to the remote site or brought along with a mobile agent to execute at the remote site. Under the new computing paradigm, how to reduce data shipment and cope with unpredictable network delay is a critical issue, we explore the opportunities that our strategies can bring to optimize the wide-area query processing as well.