Scope of Mobile Web Best Practices

W3C Working Group Note 20 December 2005

This version:
Latest version:
Previous version:
Phil Archer, ICRA
Ed Mitukiewicz, France Telecom.


Web access from mobile devices suffers from problems that make the Web unattractive for most mobile users. W3C's Mobile Web Initiative (MWI ) proposes to address these issues through a concerted effort of key players in the mobile value chain, including authoring tool vendors, content providers, handset manufacturers, browser vendors and mobile operators.

To help frame the development of "best practices" for the mobile Web this document - created by the members of the Mobile Web Initiative Best Practices Working Group ( BPWG) as an elaboration of its charter - identifies the nature of problems to be solved, outlines the scope of work to be undertaken and specifies the assumptions regarding the target audience and the anticipated deliverables. The BPWG has recently published the first public working draft of its initial Mobile Web Best Practices recommendations [BP].

Status of this Document

This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at http://www.w3.org/TR/.

Publication as a Working Group Note does not imply endorsement by the W3C Membership. This is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite this document as other than work in progress.

This third publication of the document as a Working Group Note by the Mobile Web Best Practices Working Group addresses comments generated by the previous Working Draft and marks that the Working Group believes its work on the Scope document is ready. The Working Group may publish an updated version if comments on this document make it necessary.

To send comments, please use the public mailing list (public-bpwg-comments@w3.org), an archived mailing list. See W3C mailing list and archive usage guidelines.

This document has been produced as part of the W3C Mobile Web Initiative, following the procedures set out for the W3C Process.

As of this publication, the Working Group does not expect this document to become a W3C Recommendation, and therefore it has no associated W3C Patent Policy licensing obligations. If this expectation changes, the Working Group will have an opportunity to fulfill the associated patent policy requirements with respect to a future draft.

Table of Contents

Vision for the Future

The Mobile Web Best Practices Working Group is committed to a vision of making the Web an omnipresent service platform completely transparent to its users.

This would require fully integrating the Web into our everyday lives - in a manner similar to cars, running water, central heating and telephones - so that our awareness of certain usage constraints and/or the limitations of the underlying technologies can gradually disappear.

In order to realize its full potential the Web has to be accessible via any browser enabled device anywhere and at any time. Today many of the web services and content available via desktop computers are not easily accessible through mobile devices.

An increasing variety of mobile device form factors, connectivity options and browsing constraints continues to slow down the growth of the mobile web. In order to cope with highly differentiated capabilities and limitations of mobile devices, content authors and service developers are often forced to deploy multiple versions of their offerings and/or rely on widespread use of adaptation techniques.

"One Web" vision of a seamlessly integrated Internet remains the long-term objective of the Mobile Web Initiative. Members of the Mobile Web Best Practices Working Group (BPWG) are well aware of the challenges and complexities stemming from diversity of mobile devices. However, we do not aim to address all the related issues - including many legacy problems. Our immediate goal is to define a set of forward looking Best Practices guidelines that - when followed by authors and developers - are likely to make their content accessible with equal ease to users of desktop and mobile devices of certain assumed capabilities. It is expected that this will ensure a positive user experience in both environments - within the constrains of an appropriate delivery context.

1. Introduction

As a result of widespread use of World Wide Web technologies over the Internet, a variety of content and services are now easily accessible from desktop and notebook computing platforms. Web technologies have the potential to play the same role for mobile devices. However, mobile Internet today suffers from many problems that make the Web unattractive to use for most subscribers.

The intention of the W3C Mobile Web Initiative is to make Web access from a mobile device as simple, easy and convenient as Web access from a desktop device and to facilitate advancement towards the ultimate goal of "One Web". In many respects the mobile web provides a new medium with new and exciting possibilities.

Aside from representing a further delivery channel for existing Web users, it could represent the only, or primary, delivery channel to end users who do not have access to any other Web enabled devices. Extending the reach of the Web to such people contributes to a primary W3C goal of bringing the benefits of the Web to all people. [see "One Web" statements in section 3.2 below]

Members of the Mobile Web Initiative believe that it is in the interests of all the mobile value chain participants, from content author to end user, to minimize the impact of any fixed vs. mobile differences and maximize the benefits of all the similarities.

The mission of the Mobile Web Initiative Best Practices Working Group (BPWG) is to enable the reach of the Web to be easily extended onto mobile devices. It intends to specify and publish a set of technical best practices and develop a mobileOK trustmark for Web pages that support such practices and provide an appropriate user experience on mobile devices. The best practice guidelines are intended to improve the delivery and display of content to mobile and other portable small screen-devices. For each guideline in the recommendations document [BP] there is a corresponding "How to do it" statement discussing related content development techniques. These will be elaborated further in a companion Techniques document. In addition, every guideline is accompanied by an appropriate "What to test" statement discussing the related testing issues and applicable testability criteria.

This document establishes the framework for the Best Practices guidelines, as an elaboration of the scope presented within the BPWG Charter [ CHARTER].

The BPWG does not intend to force content authors to limit the scope of their content delivery only to those mechanisms which are currently available on mobile devices. Rather, the guidelines produced are meant to enable content to be displayed as correctly as possible on a range of devices - either directly or, if and where necessary, assisted by some server, client or third-party adaptation mechanism which is transparent to the end user.

There is no intention of developing new technology, such as markup languages. However if, during the life of the working group the need for new technologies is identified, the group may raise requirements with other W3C groups or groups within other standards organizations.

2. Best Practice Dimensions and Scope

As the Mobile Web Initiative is primarily concerned with accessing content that would currently be rendered in a desktop or laptop browser, the BPWG's focus is currently on best practices that are most pertinent to "traditional" browsing. However, in future phases, the group may broaden the scope of its work in order to take into account other content presentation options that may be available on mobile devices - e.g., using the emerging multimodal technologies.

Also, whilst many mobile applications - such as Multimedia Messaging (MMS), ringtones or podcasting - remain beyond the scope of the Mobile Web Initiative scope, the BPWG should take account of the underlying service or device features, as mobile users are not likely to differentiate between similar types of content and services.

The BPWG is also striving to address issues related to internationalisation and localisation of content on mobile devices - e.g., supporting translations, enabling right to left scripts, selecting appropriate character encodings, etc.

The "Mobile Web Best Practices" recommendations [BP] draw on applicable experiences from all the mobile web stakeholders and other W3C activities such as the W3C Web Accessibility Initiative [WAI].

2.1 Expected outcomes

Members of the Mobile Web Initiative expect the following results of the BPWG work:

In both cases authors will do this either by producing simple sites that have a basic presentation effective in both desktop and mobile environments; or by adapting their content to suit the characteristics of a range of devices.

3. Assumptions

3.1 Mobile User Experience Considerations

Most of the fixed vs. mobile user experience differences stem from

An example of content issues involved is a large bitmap which contains a sports photo. The bitmap may be unsuitable for use on a mobile device and it would need to be resized or cropped, while maintaining the relevant information, such as the position of the ball.

Examples of device and access network capabilities that need to be considered because of possible technical, ergonomic or economic implications for a mobile user include:

Basic cellular radio access often offers lower bandwidth than a fixed connection
Battery capacity is very constrained in mobile devices - certain activities tend to increase power consumption and shorten battery life
Predominantly proprietary platforms from multiple vendors - based on highly integrated hardware and relatively differentiated software (e.g., operating systems) - increase capability divergences between mobile devices. Consequently, alignment of browsing capabilities becomes quite difficult, especially when transcending the existing Open Mobile Alliance (OMA) Browsing baselines.
Cellular network connectivity is commonly charged per data volume
Mobile device input capabilities tend to differ, but are usually more constrained than in desktop terminals - four-way navigation and softkeys are most common, but touchscreen-, stylus- and keyboard-based capabilities are improving. While many mobile devices offer predictive text input, data input tends to be relatively slow and cumbersome. Many mobile devices also do not offer as wide a character repertoire as desktop devices.
Significantly less working memory and storage is available on mobile devices than in desktop terminals
processing power
Significantly less processing power is available on mobile devices than in desktop terminals - hence stringent efficiency and optimization requirements that often lead to highly integrated and differentiated solutions
Small screen is a major constraint for mobile devices. Furthermore, screen widths, heights, resolution, pixel densities, aspect ratios, color characteristics and actual performance under certain viewing conditions (e.g., in sunlight) tend to vary a lot - thus introducing additional content presentation and navigation complexities. Also, as currently only a few mobile devices are capable of multi-tasking, screen is typically "owned" by one application at a time and the user interface does not support multiple windows that are common on a desktop.
Text input tends to be very slow and cumbersome on a mobile device
voice and multimodality
Voice and multimodal technologies might supplement or enhance mobile device input and output capabilities, but currently multimodality is not commonly supported and should be viewed as an emerging technology.
Given highly differentiated capabilities and constraints of various mobile devices, making the user interface reasonably standardized, simple and efficient remains the main challenge.

Similarly, illustrative context characteristics that need to be considered because of possible usage implications include:

partial attention
Mobile devices are often used in situations when the users are unable to give their full attention to the content. A user will typically be distracted within a few seconds. If there is no activity on their mobile browser for longer than that seconds, they will be lost as a user. They will often be easily distracted from what happens to be displayed at a time on their screens. Information must be concise and easily accessible.
social situation or physical environment
In direct contrast to a desktop user typically sitting alone at a desk in the office or at home, a mobile user might often be in a number of very different situations and environments - e.g., indoor or outdoor, at a party, in a meeting, on a beach, on a train etc.
The connection between a mobile device and the internet may involve a public mobile network. Such connection may drop out from time to time as the user moves into a poor reception area. Connections may also involve non-cellular networks and other wireless technologies - e.g., Wi-Fi, Bluetooth, etc.
Globally there are already more Web enabled mobile devices than computers in use. For many people mobile devices may be the only available way of accessing the Web and some of them may not even have any prior desktop or notebook Web experience.

In the light of the above, assumptions made by content authors about mobile users, their devices and usage contexts have to reflect some awareness of possible constraints and their technical, ergonomic, economic and environmental implications.

3.2 "One Web"

The W3C has already made several statements relevant to the definition of "one web."

The social value of the Web is that it enables human communication, commerce, and opportunities to share knowledge. One of W3C's primary goals is to make these benefits available to all people, whatever their hardware, software, network infrastructure, native language, culture, geographical location, or physical or mental ability.

-from About the World Wide Web Consortium [ W3C]

A URI owner SHOULD NOT associate arbitrarily different URIs with the same resource.

-from Architecture of the Word Wide Web, Volume One [ WEBARCH]

The number and nature of devices through which the Web may be accessed continues to grow. At one extreme, web content may be displayed on enormous plasma screens in public places with stadium-filling sound systems. However, the Mobile Web Initiative is primarily concerned with the opposite end of the spectrum - i.e., small, mobile devices. Given their proliferation and increasing diversity, making any general assumptions about specific device capabilities and/or particular circumstances of their use is, at best, unwise. In particular, the assumption that access to the web is primarily by means of a desktop or notebook browser and that this is the default web experience is very much open to challenge.

One recent model suggests that within three years the number of web-capable mobile devices worldwide will exceed notebook/desktop PCs sixfold. [ WOE]

Other models suggest that while the number of PCs in use by 2010 is likely to be over 1.3 billion, mobile subscriptions are expected to be on the order of 2.5 billion. [ STATS]

However, it is also noteworthy that 96.2% of an estimated 14.5 million wireless internet users in Korea also use the wired internet. [ KOREA]

The number of Japanese mobile-only Internet users has been declining recently in both absolute and relative terms. This is probably not because fewer people are using mobile access as applications such as e-mail and the download of ringtones continue to be immensely popular. Recent research suggests that if the mobile web experience is compelling, users may be more inclined to use fixed access as well. [ JAPAN]

It is often in the commercial interests of content providers to maximize the reach of their materials. Achieving this in the light of the trends referred to above means that the use of standard communication and formatting mechanisms is likely to be increasingly important. For content to be widely accessible it must not depend upon a particular implementation of standards or the end-user's choice of terminal device and browser.

That said, content providers may wish to target particular classes of user or to provide material and services that are tailored to particular situations.

This leads us to characterize "One Web" by postulating that:

The Best Practices Working Group notes that these concepts will need further refinement when considering multimedia content and certain types of devices - e.g., voice browser enabled terminal devices without a screen. These issues will be addressed in Phase 2.

3.3 Adaptation Layer

Due to increasing diversity of terminal devices the BPWG's working assumption is that multiple versions of content representation or adaptation of content to a particular set of device capabilities will be commonly used for the foreseeable future. For example, adherence to XHTML-MP can lead to different results on different devices running the same browser software. The context in which a web resource is to be displayed must therefore be addressed and hence the concept of an "adaptation layer".

As discussed above, "One Web" does not mean that precisely the same information must always be available in precisely the same way from a given URI. The context in which a web resource is to be displayed must therefore be addressed - hence the concept of an "adaptation layer" becomes an integral, if transparent, element of the Web.

In order for the adaptation layer to do its job, content must be created in a way that makes adaptation relatively simple and, critically, makes the results predictable.

The BPWG therefore strives to demonstrate:

3.4 mobileOK Trustmark and Best Practices

Development of a mobileOK trustmark is a key objective of the Mobile Web Initiative - as described in the Mobile Web Best Practices Working Group charter. The intention is to establish a set of validation tests to which content resources can be subjected. If passed - possibly subject to some content adaptation - a particular resource will be deemed to be "mobileOK". It is anticipated that this information will be presented in a visual form by means of a logo and in a machine processable form - e.g., for use by content aggregators.

The mobileOK trustmark is intended not only to help authors to create content that will render correctly on mobile devices, but also encourage software manufacturers to develop a range of compatible tools, including authoring tools and clients. The mobileOK trustmark is envisaged to have relevance across the entire content production chain.

The development of a mobileOK trustmark implies two work areas for the BPWG: defining the criteria a resource must meet to be mobileOK and defining the process and platform through which the trustmark is to be delivered.

The idea of mobileOK requires further elaboration and will be discussed in more detail in a separate mobileOK document. Best practice guidelines and the corresponding testability statements in the recommendations document [BP] are intended to provide a basis for establishing mobileOK technical requirements and conformance criteria.

Levels of mobileOK conformance in relation to different dimensions of the specified best practices - as applicable in certain delivery contexts - will be addressed in the mobileOK document. The BPWG remains open minded on how this will be achieved.

For example, different sets of mobileOK conformance requirements could be applicable to different categories of browsers - e.g., "traditional" browsers, voice-enabled browsers, etc

Also, specifications of mobileOK conformance criteria could be based on the "state of the art" practices prevailing at a particular point in time - e.g., MobileOK2005, MobileOK2007, etc.

Another option could be to specify some "backward compatible" levels of mobileOK conformance criteria - e.g., MobileOK, MobileGood, MobileExcellent - based on meeting a number of increasingly stringent best practices or their subsets or supersets.

Yet another option would be to consider different content profiles - e.g., MobileOK HTML/CSS/PNG or MobileOK XHTML/CSS/SVG/ECMAscript - or some similar compound document profile variations.

As some of these options are not mutually exclusive in nature, certain combinations of mobileOK conformance criteria might also be considered.

3.5 Open Issues

The BPWG recognizes that it is necessary to structure the work on the Best Practice Recommendations into two or more phases, with the initial focus on best practices that are most pertinent to "traditional" browsing.

The scope of Phase 2 work remains an open issue that will be addressed by a separate Phase 2 Scope document.

4. Internal and External Liaisons

The principles developed by the W3C Device Independence Working Group (DIWG) are recognized as being highly relevant to the Mobile Web Initiative. In particular concepts such as authoring units, delivery units and display units are important. The BPWG may have to extend this into a broader conceptual architecture, including for example, delivery context, device properties and geographical location. It is worth noting that the Best Practice guidelines include conditional statements in the form "if feature X is supported by the target device then a delivery unit must/should be used in this way (else in some other way)."

The BPWG will coordinate their work with the related efforts within the W3C, including:

The BPWG will also establish working relationships - based on formal liaisons, if and where appropriate - with certain organizations outside of the W3C, whose activities might impact the Mobile Web Initiative and/or be influenced by it, including:

5. Resources

The BPWG recognizes the existence of many resources that represent a considerable amount of work already done in this area. The Web Accessibility Initiative (WAI) guidelines provide an important starting point for the work to be done, for example. Further material will be fully referenced in the Best Practices document.

6. References

"Mobile Web Best Practices", see: http://www.w3.org/TR/mobile-bp/
" BPWG Charter", see: http://www.w3.org/2005/01/BPWGCharter/Overview.html
"Aug. 2005 Poweredcom article with a bar chart of Internet users in Japan (mobile-only access users shown in light-grey)", see: http://www.poweredcom.net/mailmag/front/01/03.html
" 2004 Survey on the Wireless Internet Use - National Internet Development Agency of Korea", see: http://isis.nic.or.kr/report_DD_View/upload/mobile200412_eng[1].pdf
"Computer Industry Almanac, June 2005 and Strategy Analytics, August 2005", see: http://www.c-i-a.com/pr0605.htm
" About the World Wide Web Consortium", see: http://www.w3.org/Consortium/about-w3c.html#universal-access1
"Architecture of the Word Wide Web,Volume One", see: http://www.w3.org/TR/2004/REC-webarch-20041215/#uri-aliases
"T-Mobile - Global Mobile Capex Handbook, August 2004 - modeled on Credit Suisse First Boston, Mobile Data 2004, Pyramid Research ", see: http://www.w3.org/2004/Talks/w3c10-WebOnEverything/?n=15
"WAI ", see: http://www.w3.org/WAI/

7. Acknowledgements

The editors would like to recognize the contributions of the following members of the W3C Mobile Web Initiative Best Practices Working Group (listed in alphabetical order):