Implementation And Desion Of The DOM-Based Embedded XML Parser

XML (Extensible Markup Language) is a data format, which is independent of any other language and architecture, and due to its scalability and the characteristics of cross-platform, it has been widely used among the web server and the database and has become a standard of the data description and exchange. However, because XML takes almost 80% of the processing capacity of the server, and the embedded devices of the network applications are also required the ability to handle XML, XML's flexibility is put forward higher requirements for the network infrastructure. Solving this problem is the key to improve the web service application, so that it is necessary to develop a method to alternate the software XML parsing.Through the theoretical analysis of XML parsing and the comparison of three kinds of analytical models, this paper designs an embedded XML parser of the DOM-based analytical model. SOPC system are realized from two respects of software and hardware. The realization of systematic software is parsing, parsing system is mainly consisted by four major modules: lexical analysis module, grammar checking module, DOM building module, schema validation module. The lexical analysis module is implemented by the FSM (Finite state machine), and its main function is to make the appropriate maker for the input XML document, so that the element names, the attribute names and the texts are identified. Syntax checking module is to check the syntax of the XML document, including element names and attribute names. In checking the element names, the stack structure is mainly used to match the characters of the element names; while in checking the attribute names, this paper used an efficient random access memory structure named Bloom filter, which can quickly determine whether the current element has appeared or not. DOM building module is independent with the syntax module and schema validation module, and establishes a tree structure for the entire XML document information. In schema validation module, through preprocessing the schema document, the defined rules will be made into a static table stored in memory, and the resolution process can be directly achieved the match of the defined rules of the elements and attributes of the XML document and the schema document through inquiring form to validate the XML document's legitimacy. The realization of systematic hardware is mainly consisted by:SOPC based on Nios ? soft-core processor and human-computer interaction modules. Human-computer interaction modules realize LCD display and push button selection,and gives a design of multi-function LCD display controller as man-machine interaction modules to improve system portability.The hardware of this thesis selects the Altera's DE2 board as an experimental platform. The FPGA chip model of this development board is EP2C35F672C6 and this thesis use Verilog language to realize the hardware module of the system on Quartus ? development platform. In the technical building of the Nios ? soft-core, this system has achieved the basis function of embedded XML parser, using the optimization scheme to realize parsing system, and gives the test results. The highly portable C++coding is used in system. Through a large number of experiments, the embedded XML parser designed in this paper is verified to outperform the software implementation of the XML parser, use fewer resources and have good scalability and portability.