A Twig Query Oriented XML Type Inference

With the rapid development of Internet technology, XML has become the de factostandard of data exchange and data share, and then the XML-related technology playsan important role in all kinds of XML information platforms. XQuery language is themost mainstream XML data query language developed by W3C, so XQuery engine isalso widely used in various scenarios of XML data processing. Twig query is the coreoperation of XML data query which can be perfomed efficiently by taking advantageof pattern matching algorithms. On the other hand, XML type system based on XMLSchema or DTD is widely used in the XML type checking, query optimization, viewupdate and many other fields.For some applications related XML data processing, the twig query results mayoften need to be further processed. For example, in FLWOR expressions of an XQueryprogram, the results of twig query from for/let clause will participate in thesubsequent computing expressed by return clause. The accurate type information ofthe twig query results will provide the potential for accurate type checking and moreopportunities for type related query optimization in the further processing of theseresults. The type information should conform to the structural constraints of twigpattern and the definition of their type system. This paper analyzes the issue of typeinference on twig query and proposes an accurate XML type inference approachwhich can infer the result type of twig query with high precision based on its inputdata type and the structural constraints in twig pattern. This approach includes thetransformation from XML schema graph to a kind of XML type tree, twig patternmatching on the XML type tree, a judgment of coexisting type nodes and a subtypingon XML type tree. It can provide accurate type information for different results oftwig query through different subtyped XML type trees. We provide experimentalevaluation to illustrate the efficiency of this approach.