Datasheet

Ajax Principles
As a new web application model, Ajax is still in its infancy. However, several web developers have taken
this new development as a challenge. The challenge is to define what makes a good Ajax web applica-
tion versus what makes a bad or mediocre one. Michael Mahemoff (
www.mahemoff.com), a software
developer and usability expert, identified several key principles of good Ajax applications that are worth
repeating:
❑ Minimal traffic: Ajax applications should send and receive as little information as possible to
and from the server. In short, Ajax can minimize the amount of traffic between the client and the
server. Making sure that your Ajax application doesn’t send and receive unnecessary informa-
tion adds to its robustness.
❑ No surprises: Ajax applications typically introduce different user interaction models than tradi-
tional web applications. As opposed to the web standard of click-and-wait, some Ajax applica-
tions use other user interface paradigms such as drag-and-drop or double-clicking. No matter
what user interaction model you choose, be consistent so that the user knows what to do next.
❑ Established conventions: Don’t waste time inventing new user interaction models that your
users will be unfamiliar with. Borrow heavily from traditional web applications and desktop
applications, so there is a minimal learning curve.
❑ No distractions: Avoid unnecessary and distracting page elements such as looping animations
and blinking page sections. Such gimmicks distract the user from what he or she is trying to
accomplish.
❑ Accessibility: Consider who your primary and secondary users will be and how they most
likely will access your Ajax application. Don’t program yourself into a corner so that an unex-
pected new audience will be completely locked out. Will your users be using older browsers or
special software? Make sure you know ahead of time and plan for it.
❑ Avoid entire page downloads: All server communication after the initial page download
should be managed by the Ajax engine. Don’t ruin the user experience by downloading small
amounts of data in one place but reloading the entire page in others.
❑ User first: Design the Ajax application with the users in mind before anything else. Try to make
the common use cases easy to accomplish and don’t be caught up with how you’re going to fit
in advertising or cool effects.
The common thread in all these principles is usability. Ajax is, primarily, about enhancing the web expe-
rience for your users; the technology behind it is merely a means to that end. By adhering to the preced-
ing principles, you can be reasonably assured that your Ajax application will be useful and usable.
Technologies behind Ajax
Garrett’s article mentions several technologies that he sees as parts of an Ajax solution. These are:
❑ HTML/XHTML: Primary content representation languages
❑ CSS: Provides stylistic formatting to XHTML
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