Evaluating partial tree-pattern queries on XML streams

Abstract

The streaming evaluation is a popular way of evaluating queries on XML documents. Besides its many advantages, it is also the only option for a number of important XML applications. Unfortunately, existing algorithms focus almost exclusively on tree-pattern queries (TPQs). Requirements for flexible querying of XML data have motivated recently the introduction of query languages that are more general and flexible than TPQs.We consider a partial tree-pattern query (PTPQ) language which generalizes and strictly contains TPQs. PTPQs can express a fragment of XPath which comprises reverse axes and the node identity equality ($is$) operator, in addition to forward axes, wildcards and predicates. We outline an original streaming algorithm for PTPQs. Our algorithm is the first one to support the streaming evaluation of such a broad fragment of XPath.