XML Query Technology With Positional Predicates Over Streams

As a semi-structured data description language, XML(eXtensible Markup Language) has become a widely used data exchange format and industry standard on the Internet, with its cross-platform, easy to read and write, supporting advanced search and many other features. As XML being used in various fields such as wireless sensor networks and Internet of things, “streaming XML data” has been widely studied by researchers, and brings new challenges into the field of XML query processing technology.In recent years, there are many algorithms for twig pattern matching in the field of original XML data base nowadays, and these algorithms can support a wide scope of XPath query plans. However, in the field of querying streaming XML data, algorithms can only support a very limited scope of XPath. None of these algorithms mention about the positional predicates in XPath queries, especially. Due to the lack of context information, these algorithms cannot select out the final solutions that satisfying the positional predicates in an XPath query.To tackle these problems above, the main works of this paper are:(1) Proposing a structure named“Three-tier Nested Stack” to store the context information during an XPath query over XML streams.(2) Based on the context information, proposing an implementation method to deal with positional predicates in an XPath query by using a streaming data processing method based on stack;(3) Designing and implementing PosLQ algorithm based on the three-tier stack and the stack structure, which can improve the performance of streaming XML data processing.A number of experiments show that PosLQ can efficiently handle these kinds of XPath queries, which enhances the usability of twig pattern matching technology in the field of streaming XML data.