What is CLIENT SERVER ARCHITECTURE:

Typical three architecture                                                                                                                                                                     

01.    Presentation tire

          -contains user interface

                          02. Application logic tire

                                - model & process GIS data

                          03. Storage tire

                                - Databases that store GIS data

Two types of client server  architecture

     A. Thin client architecture

      B.  Thick client architecture

A.      THIN CLINT ARCHITECTURE

The thin client architecture is used in typical architecture. In a thin-client system the clients only have user interfaces to communicate with the server and display the results. All the processing is done on the server actually as shown in fig 2. The server computers usally have more power than the client , and manage the centralized resources . besides the main functionality is on the server side in thin architecture there is also the possibility for utility programes at the server side to be linked to the server software . Figure 3 shows schematic communication between web browser , web server and GIS server . on the web server side there are some possibilities to realize the GIS connection to the world wide web . CGI , web server application programming (API) , Active server pages (APS),Java server pages(JPS) and java servlet. The descriptions of the five possibilities mentioned above are in Helali(2001).
The user on the client side does not need any knowledge aboute the linkage of the IMS at the server side , but the system administrator or application developers should be familiar with these techniques. This architecture used in ESRI ARC VIEW IMS , Mapobjects IMS and Map Info MapXtreme systems.

Major advantages of this model driven from Data Base centralization and are :

Ø  Central control

Ø  Easy for data eminence / updating

Ø  Keep the latest version

Ø  Generally cheaper

Ø  Integration possibilities

And disadvantages are :

Ø  Not responsive to local needs: user have different invokes

Ø  No local accountability: accountability need application in client side

Ø  Large data volume (size of the database)

Ø  Response time slow: users use a browser and it take time to download new HTML frame

Ø  Less interactive: in client side there is limited application and browsers abilities

         B. THICK CLIENT ARCHITECTURE

In general a web browser can handle HTML documents and embedded raster images in the standard formats. To deal with other data formats like vector data , video clips or music files , the browser’s functionality has to be extended. Using exactly the same client server communication in thin client architecture , vector files could not be used. To overcome this problem most browser applications offer a mechanism that allows thired tier progrems to work together with the browser as a plug-in.

The user interface functionality has progressed from simple document fetching to more interactive 

application. This progress is as follows:HTML,CGI<using HTML forms and CGI, java script increase user interface capabilities combined with remote invocations(fig . 4)(Byong-lyol,1998)

Major advantages of this model are;

   

Ø  Document/graphics standards are not required

Ø  Vector data can be used

Ø  Image quality not restricted to GIG and JPEG

Ø  Modern interface is possible it is not restricted to single-click operations

And disadvantages are:

Ø  Non-conformance can limits

Ø  User base

Ø  User require to obtain additional software

Platform/browser are incompatible