Study Of XQuery Optimization Based-on Rewriting Mechanism

Along with the quick development of Internet business application, XML has already become the standard format of data expression and data exchanges on Internet.Therefore a lot of business applications put forward a search to the query of XML data.Relational Database System has been almost perfect in the domain of techniques, and it's dominant in business data management area. It's been pay wide attention and regards to how to realize XML data management taking advantage of Relational Database. The keys for wide applications of XML lie in query and searching in XML data sources. It's very important to Web data management. Within a large number of XML query languages, XQuery is one part of the standard drafts of W3C(World Wide Web Consortium).And it has been used in application widely.Accordingly,XQuery processing and optimization technique is emaerging one of the main contents of XML management.It makes significant effect on the applications of XML.In this thesis,the problem is discussed mainly from three aspects:processing for query language transformation of XQuery to SQL and query rewriting based on mult-datasource and query rewriting based on materialized view. The processing course and realizing methods have been analyzed. Many current representative solutions have been compared. The feasible route to resolve the problem and to attain the requirements of application is got as the result.On the XQuery Query processing of based on relation database, I put forward akind of Mix-Processing Strategy. Mainly is the processing that transform XQuery to SQL. In fact the processing is that static analysis and type checking.,and transforming it into the SQL data structure that the localized and XML-expanded operater, and carrying on replacement on XMLQuery() function. If the XQuery expression can't rewrite into SQL, preserving the XMLQuery() function intactnessly.On query rewriting based on mult-datasource.firstly given a target schema,a mapping between a source schema and a target schema and the data of the source schema,then processing of query rewriting. The focus that paid attention to before is the relation data and schemas, We pay attention to what is the queries and mappings of the relation and XML schema now and we still need to consider to mapping of various possible scenes.According to this,I give a rewrite algorithm, involving to the rule creation, search transformation, query optimization and query integration.