Design And Implementation Of A Stream-based Xml Query Algorithm

In many fields such as Information management, E-business, Personalize publication. Mobile communication, Online Education, and Electronic data interchange, XML has been put to extensive use and has become the defacto standard for data description and exchange. As the evolution of XML technology and the spread of XML application, more and more information has been described, stored, exchanged and presented in XML. Conventional information management technology meets the challenge of XML. It becomes more important to develop the technology of querying information from XML document.After investigating the existing algorithm, we find that the implementation is based on the idea that whole XML document must be loaded into memory. While XML document is too large or cann't be loaded into memory, algorithm is of no effect. To solve this problem, we present a different method for query processing in this paper. According to the query expression, a query automaton is build, whose struct and states imply the query predicate. The XML stream is parsed into element tag and text events stream. Those events such as startelement event, textevent or endelement event trigger states transition of query automaton. To reduce memory requirement, the document fragment should be put into output immediately as soon as it meets query expression.We present a method of building query automaton and an implementation of XML stream query system. This implementation could evaluate the XPath expression in one-pass scan of xml stream. Finally we make a comparative experiment to investigate the memory use of memory-based algorithm and the steam-based algorithm.XML stream querying problem is introduced to meet the querying requirement of some data-intensive application. These applications adapt to stream data model instead of persistent data model. Stream data model can be used in many fields such as financial service, network monitor, communication data management, manufacture, sensor network. Research in this paper contributes to the theory and practice of this kind of applications.