XPath Extension for Querying Concurrent XML Markup∗

XPath is a language for addressing parts of an XML document. It is used in many XML query languages and it can be used by itself for querying XML documents. While XPath is, in general, efficient for querying individual XML documents, it lacks the features for querying over collections of documents or joining parts of the same document. As the amount of complex document-centric XML data is continually increasing, querying such documents has drawn surprisingly little attention. We propose an XPath axes extension to deal with querying collections of document-centric XML documents sharing the same content (called concurrent XML). The algorithms we propose to evaluate the extended axes work in linear time combined complexity (number of documents and total size of documents).