New devices that can connect to the web continue to appear regularly. These devices often have new capabilities and can exploit features of newer generations of networks. They are often enabled for mobile use.
As diversity increases, traditional assumptions about the design of web sites suitable for viewing on typical desktop personal computers, become less and less useful. Authors need to spend additional effort in preparing sites that can be used from devices that vary greatly in capability and in the markup languages that they support. Device capabilities vary enormously. For example, the difference between the small, monochrome screen of low cost mobile phones and the large full colour display of a typical desktop personal computer is striking. Some devices may have no display at all, supporting voice output, for example.
The variability in markup languages can be seen by examining some of the devices in common use in the United Kingdom today. Markup languages used include variants of HTML version 3, HTML version 4, various variants of XHTML, including XHTML Basic, various WML releases, VoiceXML and i-Mode. Increasingly, devices support combinations of markup for particular purposes, further increasing the variability.
In an environment where the target devices can have such a range of capabilities, authors need methods that will allow them to express their intent in a manner that remains sufficiently affordable to encourage development of a wide range of sites. The Device Independence Working Group [1] has identified a range of challenges that face authors in this endeavour [2]. It has also identified some techniques that may be applicable [3] and is engaged on developing new facilities to complement newer W3C specifications.
Approaches based on authoring methods that promote reuse, together with a strong separation of content, style and layout, hold promise and have been proven in commercial implementations. Authored materials are adapted (see [4]) for use on particular devices. Adaptation can include, for example selection of materials from alternate versions or transformation of a particular version to create an appropriate representation.
Successful adaptation requires information about how the author intends a particular piece of material to be perceived. Some of this intent can be deduced from the markup used by the author. However, sometimes, additional information may be required. As a simple example, an author might intend an image of Dublin city centre to be rendered as large as possible on the target device. Another image, of a company logo and initially the same size, might be intended for rendering as a much smaller icon. Any adaptation mechanism must be able to distinguish this kind of difference in intent in order to provide an appropriate representation.
Metadata associated with content seems an attractive method for providing this additional information where it is needed. Indeed, some experiences from work on accessibility indicate that assistive technologies can improve their interpretation of a given web page by the addition of such metadata.
Volantis Systems is keenly interested in understanding the types of metadata that might be applicable in providing additional information to improve the accuracy and quality of adaptation that can be achieved. There are many ways in which such metadata might be represented and used. Some might effectively associate a metadata profile with a resource, allowing the adaptation mechanism to select the most appropriate version. Others might annotate specific parts of a resource allowing appropriate processing to be applied during some type of transformation.
The notion of attaching some type of metadata to resources, such as documents and images, for the purpose of supporting a variety of devices has been discussed over a significant period at W3C. Volantis Systems hopes that this workshop will provide the impetus to enable work to commence on defining an appropriate set of such metadata.
[1] W3C Device Independence Working Group (see http://www.w3.org/2001/di/)
[2] Authoring Challenges for Device Independence (see http://www.w3.org/TR/2003/NOTE-acdi-20030901/)
[3] Authoring Techniques for Device Independence (see http://www.w3.org/TR/2004/NOTE-di-atdi-20040218/)
[4] Glossary of Terms for Device Independence (see http://www.w3.org/TR/2003/WD-di-gloss-20030825/)