Component Technology in the World Wide Web GIS

【Abstract]This article introduces the development and evolution of the World Wide Web Geographic Information System and component technology, and analyzes the necessity and feasibility of using the component technology to build a World Wide Web Geographic Information System, this paper mainly analyzes the operating mechanism of component models in the World Wide Web Geographic Information System. The computer hardware technology and software industry have developed at an unprecedented speed, with significant and even brand-new changes in software design ideas, design methods, model establishment, and system integration. Especially since 1990s, software networking and component-based trends have brought new opportunities and challenges to the software industry. The World Wide Web will undoubtedly provide a very broad space for the survival of geographic information systems (GIS) and provide a more extensive application on the social stage. At the same time, how GIS adapts to the development of the World Wide Web technology and uses new technologies and methods to build a World Wide Web GIS that is compatible with the network technology will be a very important issue in the development of GIS. I. World Wide Web Internet is an open Wan that connects to the world. It complies with the "Transport Control and inter-network protocol" (TCP/IP ), the World Wide Web is a new technology developed on the basis of the Internet. Its communication protocol is hyper text transfer protocol ). Texts on the World Wide Web have special requirements: ① All texts must have a unique address called "Resource Locator" (URL. ② Text is a text specially constructed using hypertext markup language (HTML. ③ The text can contain hyper link ). A hyperjoin is a URL that embeds one or more other texts (images, sounds) into one text. Therefore, the Web browser can access the URL-based text on any computer on the Internet through a super connection. Ii. World Wide Web Geographic Information System The World Wide Web Geographic Information System is the implementation of geographic information systems on the World Wide Web. It is the transformation and development of traditional geographic information systems using the World Wide Web technology. At present, the World Wide Web Geographic Information System is still in the experimental research stage. Its ultimate goal is to realize the organic combination of GIS and WWW technology. GIS becomes a widely used technology and tool through www. Specifically, on any node of WWW, people can browse and retrieve various geographical information on the Web, perform various geospatial analysis and prediction, and perform spatial reasoning and decision-making. It can be seen that the World Wide Web Geographic Information System has the following characteristics compared with the traditional geographic information system: 1. strong adaptability. The World Wide Web Geographic Information System is based on the Internet and thus global. Moreover, the World Wide Web determines that the World Wide Web geographic information system can run on different platforms. 2. wide application. Because the network function will make the World Wide Web Geographic Information System more accepted by the society, so as to apply the World Wide Web Geographic Information System to extend the whole society, and truly realize the omnipotent and ubiquitous GIS. 3. Strong current potential. The World Wide Web Geographic Information System publishes information on the Internet and updates geographic information in real time. As a result, people can get the latest information and updates. 4. Maintain socialization. Data collection, input, and spatial information analysis and publishing will work under social coordination. Maintenance of the World Wide Web Geographic Information System will be socialized to reduce repetitive work. 5. Easy to use. Users of the World Wide Web Geographic Information System can directly obtain the required geographical information from the Internet. You can directly analyze various geographic information without worrying about the maintenance and management of the spatial database.

Figure 10 thousand basic structure of GIS 3. Construct the technical route of the World Wide Web GIS 1. Use the universal Gateway Interface The Common Gateway Interface is used to define how the server and Gateway Program communicate as an Interface. On the client side, the Web browser uses HTML to create a user interface. on the server side, the GIS software system is connected to the Web HTTP server through CGI. The CGI user can send commands to the server. The server automatically transmits the commands to the back-end GIS software, and then returns the processing results to the server until the user. This method cannot meet the design requirements of the World Wide Web GIS Because CGI is not efficient and is affected by the traffic of information on the Internet, and the back-end GIS software is always running. 2. Insert Method Plug-ins is a method invented by Netscape to increase the functionality of Web browsers. The company provides an application interface (API ). Therefore, you can use a special GIS software package that can directly exchange information with Web browsers to build a World Wide Web Geographic Information System. The insertion method can enable the World Wide Web geographic information to process spatial information. However, inserting software must be installed first and then used like traditional software. It is basically an improvement solution for traditional GIS. 3. Using Component Technology (1) Component Object Model The Component Object Model is used to establish communication between software modules. The component object model provides an effective mechanism for connecting and communicating software components. In component model-based software development, applications communicate with other programs through interfaces. Interfaces must meet the binary standards of COM to support multiple interfaces. (2) Component Model of the World Wide Web Geographic Information System The service objects and functions of components in the World Wide Web geographic information system can be divided into three levels: ① Management component: component that provides WWWGIS network system functions. For example, directory management components, file operation components, event management components, and security management components. ② Service component-provides the system's GIS function. For example, the spatial data access component, the spatial analysis component, and the spatial prediction component. ③ User components: User components interact directly with users and respond to user operation requests. They are component-based abstraction of traditional GIS application modules. For example, digital component and graphic editing component. The characteristics of the World Wide Web have put forward new requirements for the World Wide Web GIS. The management component is designed to meet the requirements of distributed computing. For example, the directory management component provides a more effective way to access files to balance the distribution and traffic of online data. The security management component aims to solve online security problems, by constructing a firewall, the management component and service component reside in the firewall. In addition, the management component also registers the system of the new component and manages the lifetime of the component to ensure the security and coordinated operation of the World Wide Web Geographic Information System in a distributed environment. (3) ActiveX Component Technology ActiveX component technology is an improvement made by Microsoft Based on OLE. ActiveX components are component structures suitable for all languages based on DCOM (Distributed COM. The following uses ActiveX component technology as an example to describe the technical route of component technology to implement the World Wide Web Geographic Information System. ActiveX components can be deployed on the same network node or on different network nodes as customers who call this component. It can be run in the same process or in different processes. ActiveX DLL runs in the same process, while ActiveX EXE runs in different processes (figure 2 ).

Figure 2 running mode of ActiveX Components Figure 2 (a) shows that the ActiveX component is on the same node as the customer who calls the component, and the component object is on different processes of the same node as the customer. Figure 2 (B) shows that the component object and the customer are applied to different processes on different nodes. (4) deploying ActiveX components on the network When the customer of the component and the call component are located on different nodes, Microsoft recommends that the Distributed COM (Distributed COM) solution be used to provide the transparency of the component access. The customer does not need to change any component code.

Figure 3 DCOM Component Object Access Mode The Distributed COM Proxy/Stub object itself has the ability to communicate remotely. The World Wide Web Geographic Information System Built with component technology is easy to distribute, and programs are executed on the user end, avoiding unnecessary information traffic between users and servers, it can improve the operating efficiency of the World Wide Web Geographic Information System and the efficiency of the entire network. From the perspective of software reuse, the cost of GIS software development, development, and maintenance will be reduced. Therefore, the component technology will play an increasingly important role in the construction of the World Wide Web Geographic Information System. Iv. Conclusion With its open and friendly interfaces, the World Wide Web quickly becomes the carrier of network information processing and distribution. Effective integration with the world wide web will be the development goal of GIS in the present and future periods, GIS component models based on the World Wide Web and customer-server GIS service models are the development trend of GIS in the Network Age. The component technology effectively promotes the object-oriented technology and distributed computing technology, and plays a huge role in promoting software development and reuse. The development of the component technology has a profound impact on the world wide web. As the component technology itself is also in a stage of continuous development and improvement, building a World Wide Web Geographic Information System Using the component technology will be a process of continuous development and improvement, it is necessary to pay enough attention to this field. Author: measurement section, Beijing campus, China University of Mining and technology 100083 References [1] Li Wei et al.. ActiveX component features for Intranet distributed computing. Computer System Applications, 1998 (2): 11 ~ 14 [2] Zhang Li and others. Geographic Information System in the Internet age. Journal of surveying and mapping, 27 (1): 9 ~ 15