Research And Implementation Of Inquiry Processing And Access Control In NHX

Because of its extensibility, structure, platform independence,self-description and other characteristics, XML is now a proposed standard for data representation and exchange, more and more applacations use XML for information storing, exchanging and publishing. So Native XML Database (NXD) is brought to manage these semi-structural files. Besides, some mechanisms are needed to protect sensitive information stored in XML document, but the traditional access control technologies could not meet the requirements of modern NXD.Based on the NXD, this paper mainly puts emphasis on the access control, query language, etc. The main work and research are summarized as follows:⑴We discuss the related knowledge and function of NXD. Meanwhile, we compare NXD with traditional databases and generalize all kinds of data models used widely nowdays.⑵We design and implement a prototype of Native XML Database—NHX. It adopts the layered design method which makes the system flexible and easy to be maintained and extended. Besides, NHX adopts k-tree liked storage structure which diminishes the number of virtual nodes when the XML document is coded, so the storage efficiency is improved.⑶According to the Tree data model of XML, we present a XML area access control mechanism with flexible granularity. It makes the grain reach element or attributes level. The definition of area is simple and it can be automatic extended through user's policy. The authorization mechanism and algorithm for judging user's request are given in detail; and we have fulfilled this mechanism in NHX.⑷We design and implement the inquiry processing module and describe the Backus normal form of query language in detail. The lexical analysis uses the advanced search method while the syntax analysis adopts the top-down recursive descent parsing. Furthermore, we give some sample codes, arithmetical statement and the design of related classes.