Recent developments in information technology have resulted in a number of distributed object architectures that provide the framework required for building distributed applications. The framework also supports a larger number of severs and applications running concurrently. Many of such frameworks provide natural mechanism for interoperability (Kafatos, 1999). For example Distributed component object model architecture in windows platform and java remote method invocation (RMI) in java virtual machine (JVM) are the most popular protocols that are used in different cases. These architectures may be applied to GIS to improve the traditional client/server GIS model and develop scalable distributed GIS model. Some attempts have been made in the academic area (Zhang, 1998).
The general idea of distributed GIS service model is that a client program. In either an internet browser or an independent application, should be able to access the resources distributed in the entire network. The resources here refer to a specific machine. When it requests the remote resources during the processing is a client and any machine that provides such resources is a server. In a specific program a client may connect to servers if needed and a specific machine may be the client at one time and the server at another time. An ideal distributed GIS service model should be a “geodata anywhere, geo processing anywhere” model. Which means the geodata and geoprocessing tools could be distributed with the largest flexibility virtually anywhere in the network. The geodata and geoprocessing components do not have to be in the same site, but they should be able to cooperate or integrate whenever they are needed to finish a specific task (Yuan, 2000).
Distributed object architectures
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Microsoft's Distributed Component Object Model
(DCOM)
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Common Object Request Broker Architecture
(CORBA)
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Java Remote Method Invocation (Java RMI)
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