Design and Implementation of GIS Platform Based on the Three-tiered Client/Server Pattern

The central or two-tiered Client/Server pattern have been adopted more commonly by most of traditional GIS platform.But now,accelerated by the development of Internet/Intranet,the spatial data management and application of GIS is tending to multi-user and network distribution.The spatial data can be efficiently Stored by the improved relational DBMS such as Oracle,DB2.It is possible for us to develope the large and distributed GIS application,but the inefficiency and worse security of traditional patterns restrict this developement.Compared to those patterns,the three-tiered Client/Server pattern has more advantage,and fits the trendcy of spatial data management.It can solve the problem of effiency and security well.Above all it fits the demand of sptatial data warehouse,which will be built with the data warehouse technique and used to store and manange multiscale and spatial-temporal data in the future. In this paper,the design of this new kind of GIS platform,which is based on the the three-tiered Client/Server pattern,is introduced.This GIS platform consists of three components:the Client,the Server and the middleware.The Client has three components:the spatial data management module,the integrated GIS application and the ActiveX control.The spatial data management module is the base of client software,and includes the local issue of spatial data and communication with the middleware.The integrated GIS application,which is developed on the spatial management module directly,is GIS professional software like Editor.The ActiveX control is used to build a professional system by the developer.The middleware is a service to process the spatial data such as spatial analysis,data compression/decompression.It also provides the Client valid spatial data,which can reduce the burden of the network,and pass some command and new data from the client to the Server.The Server may be a improved relational DBMS which can store the spatial data efficiently,or a service to read and edit the spatial data file,which is stored with special format such as DXF format,Arc/Info shape file etc. The paper also shows a sample of this kind of platform,VirtualWorld software,and a application built with the VirtualWorld ActiveX control - the terrain explorer.In the application,the DEM data and the digital photogrammetric image are stored in the Oracle 8.1.6,which is installed on the Server.The three parts communicate the information with the socket. Finally,a conclusion is made that the GIS platform based on the three-tiered pattern can optimize the structure of network,reduce the burden of the Server and Client,improve the efficiency of GIS system.Also,some problems are pointed out.