Design And Development Of The Railway Gongwu Geographic Information System Based On Three-Tier Distributed C/S Structure Modes

At the end of 20th century, with the development of technology of computer and network, computing environment was trending towards distributed from centralizing. During this period, the conceptions of distributed network computing and all kinds of distributed computing modes were put forward. Among these modes, multi-tier distributed Client/Server structure mode has been widely adopted in the large-scale application system's design and exploration, and some results were achieved in these systems.Starting with the framework of the multi-tier distributed Client/Server application system, the limitation and shortages of the traditional two-tier structure are firstly discussed, and the multi-tier distributed structure is consequently introduced. Then the key technique of the multi-tier distributed structure application system, distributed mutil-database system technique, is deeply dissertated and discussed, and three-tier distributed Client/Server structure model of the RGIS based on this technique is presented. Finally, using a part of present data collecting from the DaCheng railroad and based on the devising rules of constructing the distributed application system, we emphatically discussed the concrete implementing methods using distributed mutil-tier application technique in railroad Gongwu information system of Client/Server structure, and what's more, do some work on the development of the client, middle-tier of application server and the tier of database server of the system by using the Delphi developing tool (the Borland company), MS_Access (the Microsoft company), and the graph components MapX (the MapInfo company), and so a part of functions of RGIS are realized. Compared with the traditional information systems of the Railway Gongwu department, the Railway Gongwu Geographic Information System based on three-tier distributed C/S structure mode has its advance and reference value for the later development and construction of the RGIS, as well as makes a favourabal foundation for the further deep study and development of the system.The main modules and functions of the system include: (1)User logging on module,different user's identification can be validate before entering the system for the purpose of maintaining and administering the security of the system. Since the system is based on the Railway Gongwu Geographic Information System with the three-tier C/S structure mode, it can be further divided remote server logging on module, remote database logging on module and client user logging on module. (2)Querying and Statistic module, equipment inquiring and statistical output for every Gongwu section and railway station can be performed. The querying and Statistic module of the system mainly include equipment querying, railway station querying, equipment statistic and every railway station information querying for the whole railway. (3)Graph manipulating module, the graph operating function for the railway ichnography and stations' ichnography of Dacheng railway using visualizing developing tool Delphi and MapX can be implemented. (4)Attribute managing module, the management and maintenance for the system data tables(eg. station tables, bridge tables and tunnel tables ) are achieved. (5)Report forms outputting module,using the component QuickReport of Delphi to output the report forms of system equipment and manpower resources. (6)System maintaining module, mainly involving system security and stability devising.Additionally, some key techniques and difficulties of devising and developing system, such as database management, the user-defined interfaces of system, data binding, the performance optimization and security mechanism for system, are thoroughly analyzed and studied, and the concrete solving method is also given in this paper.