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Real-World AJAX Book Preview: Design of Mobile AJAX Applications

Real-World AJAX Book Preview: Design of Mobile AJAX Applications

This content is reprinted from Real-World AJAX: Secrets of the Masters published by SYS-CON Books. To order the entire book now along with companion DVDs for the special pre-order price, click here for more information. Aimed at everyone from enterprise developers to self-taught scripters, Real-World AJAX: Secrets of the Masters is the perfect book for anyone who wants to start developing AJAX applications.

Design of Mobile AJAX Applications
Having discussed the resurgence of browser-based applications and the significance of AJAX widgets on mobile devices, we'll turn to the design of AJAX applications/widgets.

Traditionally, standards on the mobile Internet were driven by OMA, the Open Mobile Alliance (www.openmobilealliance.com). With AJAX and Web 2.0, for the first time we're seriously entertaining the possibility of the "One Web," a seamless Web spanning multiple devices and delivering the same information regardless of the device that's used to access it.

As might be expected, the One Web concept is driven by the Internet as opposed to the mobile Internet. The standards bodies governing the idea of One Web are the same as the Internet standardization bodies like W3C (www.w3.org/). W3C is working with other bodies like OMA to deliver a consistent set of One Web recommendations.

Per the W3C documentation, One Web means making, as far as is reasonable, the same information and services available to users regardless of the device they're using. However, it doesn't mean that exactly the same information is available in exactly the same way across all devices. Some services and information are more suitable to and targeted at particular user contexts.

In W3C, the W3C mobile Web initiative (www.w3.org/2005/MWI/Activity) and the Mobile Web Best Practice (MWBP) Working Group (www.w3.org/2005/01/BPWGCharter/Overview.html) are working towards the One Web goal. While some of the standards and guidelines produced by this group are still under discussion, they provide a good basis to design a mobile browsing application and by extension a mobile AJAX application.

The mission of the MWBP Working Group is to develop a set of technical best practices and associated materials in support of developing Web sites that provide an appropriate user experience on mobile devices.

The working group aims to extend the reach of the Web to mobile devices by providing guidelines, checklists, and best practice statements that are easy to comprehend and implement. When implemented by a Web site provider, they will enable users to get the content on mobile devices, particularly small-screen devices such as PDAs, smart phones, and touch-screen devices.

The working group expects to maintain contact with groups such as the Open Mobile Alliance.

Besides creating recommendations and best practices for the One Web, W3C is also working towards the concept of a Mobile OK trustmark. According to W3C the trustmark will serve as the main conformance claim for the best practices document.

By definition, mobile AJAX applications are mobile Web applications. The impact of the preceding discussion is that when we consider the design of mobile AJAX applications, we have to consider it in two facets: the design of a mobile Web site as recommended by the W3C and AJAX-specific considerations as applicable to mobile devices.

To design mobile AJAX applications, we first have to understand W3C's standardization efforts and then the specific factors relating to mobile AJAX.

Also note that the W3C recommendations discussed here pertain only to site usability. In a broader context, usability can be defined as comprising three parts, namely, site usability, device usability, and browser usability. According to W3C definitions:

Site Usability relates to the structure, content, and layout rules of a site and is a measure of the effectiveness of the mobile Web site.

Device Usability pertains to the capability of the equipment being used easily and effectively.

Browser Usability defines the ease of using a browser effectively and doing the functions of reading, navigating, and interacting. The ease of interaction, page rendering, and caching are issues that are frequently used to judge browser usability. Device usability is determined by the device maker and browser usability is defined by the vendor creating the browser.

Factors Affecting the Design of Mobile Browsing Applications
The factors affecting the design of mobile browsing applications are:

Presentation Issues: Because Web pages are created to be displayed on desktops, they can't be presented directly on the mobile device in their original form. Not only is the overall user experience poor, but the content doesn't lay out as originally intended due to the different screen size.

Input: Mobile devices have limited input capacity and it's hard to type in long URLs. In some cases, there's no pointing device, as in some phones, and in general, it's hard to recover from errors.

Bandwidth and Cost: Mobile networks can be slower than fixed line networks. They have a higher latency and in most cases the user pays for data retrieval. The device may support limited types of content. The user may download content only to realize that she can't use it. The user may download content and have to pay for additional data such as advertising. All these factors degrade the user experience and usability.

User Goals: Unlike Web users, mobile users, have a definite purpose when they browse. Web users browse for fun or to explore a topic without a specific goal. The mobile user seeks a specific piece of information and wants it delivered in a format suitable for the device, in other words, a short/exact response to the information request that can be rendered on the target device.

Advertising: It's necessary to be extra vigilant when it comes to ads on the mobile Internet because they can potentially hinder the user experience and may not be free because the user pays for the data download charges.

Device Limitations: Mobile devices impose limits due to screen size and limited input capabilities. There are other limitations from the restrictions on the software that can be executed on a device. In practice, this means browsers can support limited or no plug-in or scripting capabilities

Some activities associated with rendering Web pages are computationally intensive. For example, reflowing pages, laying out tables, processing unnecessarily long and complex stylesheets, and handling invalid mark-up. Such compute-intensive applications push the capabilities of the battery, memory, and communications.

General Design Principles
Establish the Context of the Device: It's necessary to take all reasonable steps to find the capabilities of the target device so that the content can be served to the device in the most suitable form. The techniques used to find the capabilities of a device are beyond our scope but they include CC/PP or Composite Capability/Preference Profiles (www.w3.org/TR/CCPP-struct-vocab/), UAProf or User Agent Profile (www.openmobilealliance.com), CSS Media queries (www.w3.org/TR/css3-mediaqueries/), DDWG output (www.w3.org/2005/01/DDWGCharter/), and DIWG material (http://globalchange.gov/policies/diwg/diwg-summary.html). When insufficient information is available, reasonable defaults should be used.

Exploit Client Capabilities and Don't Take the Least Common Denominator Approach: If a better user experience can be obtained by using the device's capabilities, the W3C recommends that the developer exploit such capabilities.

Work Around Deficient Implementations: The developer should take reasonable steps to work around deficient implementations. Because the software in mobile devices is frequently embedded in the device, there's no easy way to correct or enhance software once it's in the field. So some browser implementations will have known limitations and the developer should cater to them as best he can.

Content Adaptation
Devices can differ in terms of mark-up, image format, image size, and color depth. Hence content has to be adapted so it can best be rendered on the device. The process of altering content to cater to the widely varying characteristics of mobile devices is called content adaptation. Content adaptation is a complex process and its full scope won't be covered here.

In the easiest cases adaptation can be simple and consist of just determining the device type and then choosing content from among a set of previously prepared content appropriate to the device characteristics.

The other extreme involves dynamic content adaptation with the actual content formatted at the time of image retrieval. The adaptation itself can be carried out at three different points: server-side content adaptation, network adaptation, and client-side content adaptation. Currently W3C documents cover only server-side content adaptation.

From a design perspective, the content adaptation section of the W3C recommendation is interesting because it gives us the default delivery context, which represents the least common denominator when sufficient information isn't known to do content adaptation.

The default delivery context is defined as follows:

This content is reprinted from Real-World AJAX: Secrets of the Masters published by SYS-CON Books. To order the entire book now along with companion DVDs, click here to order.

More Stories By Ajit Jaokar

Ajit Jaokar is the author of the book 'Mobile Web 2.0' and is also a member of the Web2.0 workgroup. Currently, he plays an advisory role to a number of mobile start-ups in the UK and Scandinavia. He also works with the government and trade missions of a number of countries including South Korea and Ireland. He is a regular speaker at SYS-CON events including AJAXWorld Conference & Expo.

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