Research On XML Query Technology

XML has become new criteria of data representation and exchange in Internet and it has been accepted in many fields since it was put forward by W3C in 1998. With wide adoption and development of XML as a description language for document and information, users will have more requirements for performance of XML query.Although great achievements of XML research have been made, there are many problems of XML query technology because of XML inherent characteristics. This paper focuses on XML queries, aiming at solving following problems: 1) How to construct an XML query while saving the users' trouble of learning complicated XML query language when they use it. 2) How to construct an XML query without the necessity of learning the detailed structure of XML documents to be searched? 3) How to improve the accuracy rate while guarantee the recall rate in XML query?The main works of the thesis includes:1. This paper puts forward a new method of storing XML data in relational database, which makes use of information of DTD.XML documents based on different DTDs can be kept in the same relational table. All DTDs are keeped in the same table. Therefore, only two tables are needed.2. Considering the inherent characteristics of XML documents, the applied environment and matching requirements for XML query, this thesis puts forward an XML query project which divides the XML query into two parts, the content query and the structure query. In this project, XML documents can be handled as the traditional text file in order to achieve the contents query, at the time accomplishing the task of structure query.3. In structure query, a new method is brought forward for calculating the editing distance, which is called XQED (Editing Distance for XML Querying) and is suitable for measuring the similarity of the querying tree and the structure of the XML document. In this method, the DTD will be trimmed in order to pick up the efficient structure, comparing to the querying tree which is regarded as reference. The editing distance between the structure which is picked up and the querying tree is considered as the XQED between the DTD and the querying tree. This method is proposed in the condition of fully considering the applied environment and matching requirement, thus it is more suitable for XML query comparing to other methods for distance calculating.