Xml Query Processing Structures, A Logic Optimization Algorithm

With extensive appliance of XML to many fields such as Information management, E-business, Personalize publication, Mobile communication, Online Education and Electronic data interchange, XML has become the defacto standard for data description and exchange, more and more information has been described, stored, exchanged and presented by XML. However, the query of semistructure-based XML data is different from the relational database query. Accordingly, the efficiency of query is affected a lot. Currently, lots of XML data is stored in the file form on the internet. Although this method is very simple, the query is inefficient, and can not satisfy the query of complicated structure. So, there are so many problems in querying of XML data efficiently and accurately.Query optimization is an important issue in database, it is the key method of querying efficiently. Firstly, query language is changed into an inner expression (usually is query algebra such as relational algebra or XML algebra), get the equivalent expressions by rule, then compute the cost of different expressions and choose the lowest one. This is query processing. The research on query processing is the key to query optimization, and one of the most important things in query processing is logical optimization. So, in this paper, we research on logical optimization.In this paper, we make some researches on the XML query structure and analyze the optimization policy in logical optimization. How to optimize the path expression is discussed primarily in this paper. Path expression is one of the core components of most XML query languages. However, there are few researches on the issue of path expression optimization. In this paper, a kind of path expression optimizing principle is proposed by illation, named path shortening method. We compare the Path Shortening and Extend Join, and then test them with the standard of evaluating.The research in this paper is as follows:(1) We analyze the XML query processing and research on the optimization policy in logical optimization.(2) A new logical optimization principle is proposed by illation. This new logical optimization principle is Path Shortening.(3) Introduce the standard of evaluating, test and evaluate Path Shortening, analyze the experimental result.We compare Path shortening with Extent Join, the experimental result show that the XML query efficiency is improved by Path Shortening and Path Shortening is much better in extendibility than Extent Join. So, we can say that Path Shortening can be used to join operation of large data set.