Research Of Recursion Optimization In XQuery Based On Twig Pattern Matching

As a semi-structured data description language, XML has been widely used on thedata storage and exchange on Internet. For querying and processing XML data,XQuery language is recommended by W3C as the standard query language for XML.Due to the widely using of XML and increasing data size, efficiently processing ofqueries in XQuery has been studied intensively in recent years.XML can be used to store data with recursive data structure. User can definerecursive function in XQuery for querying and processing the recursive data. Theimplement of XQuery query system can optimize the recursive function. XML twigpattern query is considered as core operation for querying XML and a key toefficiently implement XQuery. By using twig pattern, the holistic twig patternmatching algorithm can match query result from XML document efficiently. Morepowerful recursive queries can be achieved via combining recursive function and twigpattern query.For each level of recursive function call, the structural constraints among targetXML nodes described by query expressions are identical. If a twig patterncorresponding to the whole recursion can be extracted from the recursive function, thequery results that each level of recursive function calls need can be matched by thetwig pattern.To optimize processing of recursive query, this paper proposes recursive twigpattern query to extend traditional twig pattern query with recursion and an effectiveholistic twig matching algorithm for the recursive twig pattern query. Results ofexperiments show that this approach can improve query efficiency and eliminateredundant intermediate results.