| Nowadays, XML has become an important standard of information exchange and denotation in Internet. The emergence of great lots of XML documents, especially, the Native XML database, has flung down a challenge to scholars in the field of database. How do we extract information from the Native XML database efficiently and accurately has become a study hotspot.It is inefficient to query XML data in XML database using the traditional method which scans the tree structure continually, it can not meet the complex processing request. The subject does a close study on the optimization of path expression. The purpose is to simplify the model of the tree. Therefore, in order to enhance the match efficiency, we need to use the optimal technologies to the XML database, simplify path expression. Meanwhile, we must decompose query expression and resolve complex query into many simple queries, it also must promise that its query result is effective.Aiming at the query optimization of Native XML database, the main contents and contributions of this subject are summarized as follows:(1) The introduction of XML-related technologies, comparison of XML data storage and query. This paper will adopt the way of native storage, in view of the advantages and disadvantages of several methods.(2) The disposal of path expressions. As to the reverse axes in path expressions, this paper will present to rewrite the reverse axes, so that we can reduce the type of dealt axes and avail the estimates of path expression. Aiming at the existence of redundant nodes, this paper put forward the minimization of path expression basing on the implication theories, which reduces the size of patterns tree and increases matching efficiency. Moreover, this paper will decompose path expression in order to ravel out expensive matching in accordance with certain rules.(3) Finally, by designing a prototypic system and comparing the proposed method with others, it indicates the proposed method is more efficient. |
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