What is the relationship between Mobile AJAX and Mobile Widgets?
In its entirety, AJAX is comprised of XMLHttpRequest + DOM Scripting + XHTML/CSS. Functionally, two things are happening here: data is being fetched asynchronously and the information thus fetched is being rendered on the client through JavaScript.

Most widget engines are using the asynchronous part uniformly but are making their own changes to the rendering (display) part. While this leads to fragmentation of widget technology, the fact still remains that AJAX, i.e., Asynchronous I/O and visual rendering, are the core technologies underpinning widgets.

When it comes to the mobile environment, we are seeing the same phenomenon, i.e., we see Mobile Widgets powered by Mobile AJAX and also some fragmentation. Also, it should be noted that we are seeing the first attempts at standardization of widgets from the W3C.

Which browsers support Mobile AJAX?
This is the list of currently known mobile browsers supporting AJAX, which means they feature the XMLHttpRequest or an equivalent ActiveX (as in the case for IE Mobile). Some of these browsers currently exist and are widely used; others are in development and are not yet available.

• Opera Mobile (>= 8.x, not Opera Mini)
• IE Mobile (WM 5.0/2003)
• S60 3rd ed. (WebKit/KHTML core)
• Minimo (Mozilla based)
• OpenWave (>=Mercury)
• NetFront (>=3.4)
• Safari Mobile (iPhone)

It should be noted that support for the XMLHttpRequest object or ActiveX is usually not enough to fulfill AJAX tasks. The browser needs to support JavaScript to a level that it can manipulate and display the retrieved data via the DOM, although innerHTML support can be enough in many cases. CSS support is also a rather important feature, e.g., to hide some content areas and show others.

There are also other devices than phones that feature Web browsers to look at, for example, gaming consoles, such as the Nintendo DS and Wii or Sony’s PSP or PlayStation 3. These devices – partly mobile, partly fixed – feature Web browsers (Opera for Nintendo, NetFront for Sony) that are comparable to those found on mobile devices such as cell phones. Some of these constrained browsers support AJAX (for instance, Opera browsers in Tranzas set top boxes). Another significant similarity is that these devices also feature very constrained input methods, sometimes less than on cell phones, e.g., four buttons and a four-way directional pad on the PSP.

Which enterprise applications employ Mobile AJAX?
SoonR is one of the early pioneers of Mobile AJAX and seems to always be the preferred example. The SoonR application is primarily concerned with access to files on the desktop from a mobile device. It mainly supports Opera Mobile and S60 3rd edition for AJAX functionality, but there also is a basic version for other browsers without AJAX. Enterprise applications offer an opportunity for Mobile AJAX because they provide a rich browser-based experience on a mobile device and, at the same time, are not constrained by the need to access device APIs (for instance pPhone book APIs on a phone).

What is the role of the Apple iPhone with respect to Mobile AJAX?
While this is speculative since enough details of the iPhone are not known, Apple has said that the iPhone will not include Java and may include Flash. It is very likely that the Web browser of the iPhone will support AJAX. If that happens, then widgets could play a major role on the iPhone with Mobile AJAX as one of their enabling technologies. If so, it would help the uptake of Mobile AJAX post launch of the iPhone.

How do applications like mojax or bling software fit in?
Mojax and Bling Software are examples of applications that use Mobile AJAX with Java as middleware. AJAX makes a great presentation layer, but isn’t ideally suited for working with device-level APIs (Bluetooth, camera, XML, etc.) where technologies such as J2ME/BREW/C++ are already being used extensively. Thus, it is possible to use the combined strengths of each technology (J2ME + AJAX) to create the best experience possible.

While not leveraging open standards exclusively, these applications can very well make sense and they show that AJAX technology is a major building block in application development – either based on the Web browser or on a Java/C++ application.

In fact, Sun is taking a similar approach with its Java FX technology.

How can you develop for and test on all those browsers?
Much in the same way you develop for the Web today: use Web standards, then find a good reference browser (Opera Mobile, Nokia s60, Internet Explorer Mobile, etc.) and use it constantly throughout development. To maximize compatibility, plan to build a normal mobile Website (without AJAX) and progressively enhance it with AJAX as required. Test the site or application on basic phones (WAP 2.0, XHTML-MP – no DOM/XHR) to be sure it works for existing non- AJAX capable browsers.

What are the (current) hurdles in implementing and running Mobile AJAX applications?
The biggest obstacle is the same as on the desktop: browser support. With more browsers than on the desktop and bigger differences in their support for Web standards and technologies required by AJAX, this poses a real problem and has kept many developers from going any further than initial tests.

Another technical problem is HTTP latency. Loading only parts of the Website in a mobile Web application can take as long as loading the whole page (still traffic and rendering time in the browser will be smaller). This varies from one connection type to the other and can also be influenced by the carrier’s implementation of their proxy.

Also power consumption and battery drainage of AJAX applications can be an issue. If an AJAX application constantly connects to a Web resource, e.g., to check for new data, this will not only drain the phone’s battery heavily, but may also incur expensive data fees for some users. So AJAX functionality has to be applied in a responsible and meaningful way, especially in applications running on mobile devices.

Mobile AJAX and Mobile Widgets, while showing a lot of promise, are still currently geared toward simple tasks and applications.

What are AHAH / AJAH?
The desktop computer has much more memory and CPU power as well as different means to input data into the application. Mobile AJAX has to work on resource constrained devices and browsers, so typically most desktop AJAX libraries cannot be used on mobile browsers. Instead of sending and manipulating raw XML on constrained devices, it makes a lot of sense to leave the manipulation of XML to the server and send only XHTML to the client.

This technique, while very similar to AJAX is often called AHAH – Asynchronous HTML, and HTTP – or AJAH – (HTML instead of XML). Fundamentally both methods do not transport XML, but pre-rendered HTML or XHTML, and avoid having to process XML data on the client, which can be a very battery- and CPU-intensive operation.

Is there any standardization initiative for AJAX?
While not a standards body, the Open Ajax Alliance is bringing different players in the industry together (and this also includes Mobile AJAX).

Feedback Requests and Enhancements
We welcome feedback and enhancements requests. If your company is doing some interesting work in this space, we can consider adding it to this FAQ. Please contact ajit.jaokar at futuretext.com for any suggestions.

Acknowledgments
We would like to acknowledge the work of the following people/groups:

Eli Dickinson, editor, FierceDeveloper
C Enrique Ortiz
Daniel K. Appelquist
The Open Ajax Alliance