XPath Selectivity Estimation for a Mobile Auction Application

Whenever nodes in a mobile network try to access an XML database server, the offered data must be somehow queried and transported by a mobile network to the querying node. For this purpose, two mechanisms are possible: query shipping and data shipping. Which one is better depends among other aspects on the query result size, more precisely on the overhead that data shipping incorporates compared to query shipping. In this paper, we present a query result size estimator that allows each mobile user to estimate the resulting size and cardinality of an XPath query by means of special distributed meta data in order to decide between query shipping or data shipping by comparing the estimated size of the result with the data that must be requested for data shipping. We show how the meta data is generated for certain query classes, how the meta data can be used to predict the result size and cardinality, and we give experimental results on the deviation of the predicted results.