A Study On XML Query Method

With the development of modern scientific technology, XML has come into a rapid development period and an absolutely necessary tool in the fields of official business, management and decision-making which draw more attention with the development of network. At the same time, XML, as the exchange center and integration of multiple data source, has been mature gradually. Because of broad application in the web, it seems quite important of data query based on XML files themselves. At present, the method based on XML data storage and query is commonly grounded on the structure of tree and relational database. If XML files are described as a tree, though the path expressions are legible, the data quantity of the tree is big so that the speed of query is influenced. If XML files are directly saved in the relational database, though the structure of relational table is canonical and the speed of query is something raised, the flexible property of XML files structure may be lost. The path expressions are made up of XML elements or attributes, which are the essential part of XML query Language nowadays. It has been one of the hot issues of XML research based on path expressions query efficiency.A method is proposed for modeling XML Semantic Structure with a Petri net. In other words, the structure and the data of XML files are modeling respectively. A Petri net model is constructed based on XML DTD, i.e. modeling XML Semantic Structure with a Petri net. Element declare and attribute declare are described as some transitions in Petri net. Elements and attributes are described as places in Petri net. The path expressions in XML query are described as Tokens in Petri net. XML data are saved in relational database based on the structure of a Petri net. XML query is translated into the query of relational database by Petri net and come true accurate location of XML path expressions. The efficiency of XML path expressions query can be improved. For instance, the result of path expressions query such as "//element]/element2/element3/.. ./element_n"is O(n).At last, through detailed examples, a book query system was especially designed via the aforementioned research methods and technical routes to describe the structure and data of book's XML files respectively. According to designed flow chart, compile codes, run programs, a book query system based on a Petri net was completed.