The standard client/server model applies, in one form or another, to all DGI applications. The basics are as follows: the client program (usually a web browser such as Netscape or Internet Explorer) makes a request to a server (or a web page) by using that page's URL or internet address.
The server then processes that request and then returns information to the client. This is the model upon which most basic web pages operated. However, for a DGI application to operate, a slightly more complex model must be employed. This model is called the multi-tiered server. It is based on the first model but adds another level of communication to the client and to the server which interacts with the GIS software or database.
The client makes a request to the server, the server interprets it as a DGI request, sends it to a DGI program at which point it is translated into computer code. The DGI program then sends the encoded information to the GIS software which, in turn, returns the appropriate information to the DGI program. It is then reformatted into a form that the browser can recognize and sent to the original client.
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