Multi-layer Structure Webgis Based On Component Technology Research

Networked and Componented are two important tendencies of Geographic Information System (GIS). With the development of computer, network, distributed object and component tecnology, the difference between them is increasingly vague. Based on object-oriented methodology, component make the complicated and huge system can be assembled by divided components, and the components developed by different developers can be integrated in one system. The technology of distributed object provides a new developing method for WebGIS. Comparing with traditional development, it can be more efficient and functional. With the support of distributed computing, multi-tired WebGIS has been a research area of interest. The development of multi-tiered WebGIS based on components has become a focus due to its strong flexibility and adptability.The first part of the paper introduces the architecture of multi-tiered WebGIS based on component, describes the tiered pattern in detail, and discusses the application of tiered pattern in building WebGIS. Meanwhile, the paper analyses some main standards of distributed component, such as COM/DCOM, CORBA, and discusses current status of componented WebGIS, points out it is the future mainstream of WebGIS that the way tiered and componented are combined.In the latter part, on the base of the analysis of some commercial WebGIS solutions, the paper proposes a 5-tiered WebGIS architecture model which is independed on the platform. The model is extensible and maintainable. Cooperating with certain network software bus, by adding business components to it, the software system may adapt to a variety of changes by simple deployments. Compared with the complicated, hermetical structure in traditional development, the model can effectively improve the reusability and portability of the system. Based on the model, using COM/DCOM and XML, a WebGIS prototype system is constructed. To illuminate the resegmentation of complex tier, the paper describes the design and implementation of the representation tier. At the same time, the paper introduces XML and its correlated technology in detail. XML is increasingly important in WebGIS. In the multi-tiered componented system, XML is exerted in many places. The implement of the prototype system takes the exptensibility and flexibility into account. The whole software system has clear tiers, perspicuous structure, favorable flexibility and good retractility. All these traits help the system to avoid many problems of maintenance and upgrade generally caused by traditional development.