Geoscience Reference
In-Depth Information
Classic Web Application Model (synchronous)
CLIENT
user activity
user activity
user activity
TIME
system
processing
system
processing
SERVER
Ajax Web Application Model (asynchronous)
CLIENT
browser
user activity
Ajax engine
client-side processing
TIME
server-side
processing
server-side
processing
server-side
processing
server-side
processing
SERVER
Fig. 13.5 The typical client-server communication is synchronous (top illustration). AJAX uses
asynchronous communication between the client and the server. A connection is maintained to the
server to speed interaction
the start of a web session, the AJAX engine is initially loaded in the background.
Once loaded, the JavaScript code downloads data from the server without refresh-
ing the web page. A user action that normally would generate an HTTP request to
the server becomes instead a JavaScript call to the AJAX engine. If the engine can
respond to a user action, no response from the server is required. If the AJAX
engine needs something from the server to respond to a user request—such as
retrieving new data—the engine makes the request without interrupting the user's
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