Research On Query Optimization Technologies In XML Database

With the development of Internet, XML has gradually become the standard for data exchanging on Internet, it has also developed a new field for the application of database—XML database. However, the semi-structure characteristic of XML data and the difference between the query of special XML path expression and the structured query language of relational database, make the query optimization technologies of the relational database no longer applicable for XML database. Therefore, XML query optimization technologies become an important field in XML database research.This thesis researches the query structure of XML database, and analyzes the steps of the query processing, which focuses on the strategy of logical optimization and physical optimization. Then, it researches three methods of query optimization technologies of XML database. They are optimization based on path index, optimization based on encoding and optimization based on XML Schema.Optimization based on Schema is an important method of XML query, which can cut down the query expression by the information of Schema to optimize the query of XML. This thesis brings forward a kind of XML optimization technology based on XML Schema—XSIS. XSIS introduces PBiTree encoding and region encoding to encode XML Schema document and XML document separately, and builds indexing for schema document and XML document, then introduces the processing of querying in XSIS. XSIS also brings forward a kind of building Reduce-Tree to resolve the loop of XML Schema. This thesis also compares the response time of querying between XISS and XSIS. Finally, this thesis shows the discussion of multi-Schema technology based on the research of single-Schema optimization technology.