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1.5.1. Extended Client-Server Architecture

Thick and Thin Clients

The WebPark platform was designed around the so-called "Client-Server" architecture. The idea of this is that a client, which might be a web browser on a mobile device or personal computer, accesses data over the internet from a server which acts as a repositiory for the information. The client and server communicate using agreed standards such as those defined by the OGC. Refer to the lesson OGC Standards and WMS for more information about this. Clients can have different "thicknesses" depending on how much processing work they need to do to present the data provided by the server. A thin client might request data that is returned as a graphical image file (e.g. png or jpeg). In this case it needs to do little work except display the image to the user. Instead the server will have performed all the processing necessary to draw the data correctly. A fat client will access raw data and need to perform much of the rendering operations itself. The problem for location-based services such as WebPark is that they cannot rely on a continuous internet connection. This makes it difficult to employ a straight forward client server architecture. WebPark uses the termcaching technique to dissove the problem. To decide which data to display the WebPark client needed to be little fatter than in an always online scenario, but not so fat that it needed to perform large amounts of processing to render the data. The illustration below describes the basic pattern, together with some of the processing operations performed on each side.
Extended Client-Server Architecture used in WebPark



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