Anyone who has ever shopped for cars on the web has undoubtedly noted the following behavior. You are presented with a drop-down list of brands (Acura, BMW, Chevrolet, Dodge, Ford, etc.) and you choose the brand of car you are interested in. You then move to the next drop-down list, which is model. If you chose Acura in the first list, you will be presented with a list of Acura models (RL, TL, TSX, etc.). But if you chose Ford, you will be presented with a list of Ford models (Focus, Fusion, Taurus, etc.).
Now the average person will see this behavior and say "So?" This works exactly the way it should, so its behavior is as expected. The person with a basic understanding of how the web works may note "Hey! There was no web page loaded in between using the two drop-down lists, and yet the choices changed. Pretty cool." But the beginning web designer will likely be surprised. How could the page have changed without reloading it? And how can I learn to implement this technique for interactive web applications?
In this article, I will present an overview of one of the most popular techniques for producing web sites that are interactive, and that present the user with choices that make sense in the context of what he or she has already done since the page was loaded. This set of techniques allows a site to perform better by minimizing traffic between the client machine and the web server.
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