Optimized Internet Search Based on a Intersection Test for XPath Expressions under a DTD

Whenever XML data is distributed over several web sites but follows a global schema defined by a DTD, i.e. multiple sites contain fragments of a global ‘virtual’ XML document, and the accessible XML content stored on a site can be described by an XPath expression, it may be considerably advantageous to search for XML data only on those sites which contain a relevant fragment of the distributed XML document. Our optimization uses the XPath expression which describes the XML content of a web site and the XPath expression given in a search query in order to decide, whether or not the site has to be searched for relevant XML data. This is done by testing whether or not both XPath queries select disjointed node sets. The key idea is to transform each of the XPath expressions into a graph which contains all paths selected by the XPath expression. Thereafter, an intersection graph is constructed for a pair of XPath expressions. Within this intersection graph, we search for a path which is compatible to all the filters attached to the XPath expressions.