Basically, a Browser/Server (B/S) model is adopted in the system design where nearly all computing load is located on the server side, while the client side is only responsible for displaying. In this project, SOA is used to facilitate data communication and interactive operations for the reason that each web service is an independent unit in SOA. The general structure of the web-based UMS using SOA is described as follows (Figure 2). In Figure 2, the server side is composed of GIS web service providers, an image cache server, a web server and a firewall.
Figure 2. Structure of web-based UMS using SOA
In response to the two basic types of urban data at the City of Windsor, two GIS web service providers are devised, respectively a vector data service provider and an aerial photo service. Web service providers are computer servers to publish maps. The vector data service provider is an Object-Relational Database (ORD) based server where all GIS vector data is stored and indexed. The aerial photo service provider is a RDMS based server. High resolution aerial photos are stored in RDMS as pyramid images that can accelerate data distribution at different scales. ArcSDE, a middleware that can facilitate data management, data transfer, and data interaction in one RDMS or among RDMSs, is used to help the data communication between the database servers and map servers.
In order to enhance the efficiency, an image cache server is placed in this system. Maps are usually static, but most map servers render WMS data every time they are queried. This situation can result in unnecessary processing and increased waiting times. In this UMS, an image cache server is added to store all map tiles. When a user requests a map from the cache server...
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...online mapping and the mapping on a local machine is minimized.
Additionally, Java Servlet technology is employed to develop certain modules. Java Servlet is a server side procedure, which can respond HTTP requests from the client side. It provides a simple, consistent mechanism for extending the functionality of a web server and for accessing existing business systems (Vandana, 2001). In this project, the printing functionality is developed based on Java Servlet. When a client wants to print the current map and sends the request to the server, the print server will run the print servlet on the server side and respond the client with the requested map in PDF format. The use of Java Servlet can further transfer computing load from the client side to the server side in order to make the client perform only simple tasks, such as sending requests and downloading PDFs.