W3C DIWG Delivery Context Workshop

4-5 March 2002

Position Statement by Volantis Systems Ltd

Author: Martin Jones, Head of Device Research.


Volantis builds software that enables presentation of a single web site on a wide variety of different devices.

The Volantis approach is based on a device-independent markup language together with a repository of device-dependent information. The information stored in the repository includes explicit details of the physical layout of pages on various devices as well as definitions of the styles to be used. In addition, the repository holds device-independent abstractions of device-dependent content, such as images and other multimedia. The repository also contains detailed information about the characteristics and capabilities of each supported device. This information is used in creating appropriate pages to be delivered to each device. It is also available for applications that use the Volantis technology. Volantis has taken particular care to organise the repository so that, where appropriate, information such as style and layout can be shared among families of related devices, minimising the effort necessary for applications to support them.

This approach, based on device-independent markup and strong abstractions of device capabilities and of device-dependent information, has proven highly scalable to large numbers of devices. It is also highly agile, enabling existing sites to support new devices with little or no change.

Involvement with W3C

Interest in Delivery Context

Understanding and conveying delivery context is seen as a major plank that is necessary to support device aware web presentation. Current mechanisms that can be exploited to determine some elements of delivery context (such as HTTP User-Agent and Accept headers) are limited in various significant ways. Other elements of delivery context, such as user preferences, are not currently provided at all in a standardised way.

The aspect of delivery context of most immediate interest to Volantis is the robust conveyance of device capabilities/attributes and user preferences from the user agent to the origin server. However, all aspects of delivery are potentially relevant. For example, although Volantis' technology is currently designed for use in origin servers rather than proxies, there are alternative architectures (e.g. portals) where Volantis products can be used as part of an intermediary in the content delivery chain. Volantis may need to concern itself with the properties and behaviour of other servers, both up and down the delivery path.

Barriers to the Adoption of Delivery Context-Related Standards

Volantis is primarily concerned that any standards that are developed to provide, convey and use information about delivery context should be widely adopted. It is vital that such standards should not be too onerous to implement for any part of the delivery chain.

It is important to consider the (often conflicting) demands, not only on user agent and origin server developers, but also the developers of intermediaries such as proxies and gateways.

Also, it is necessary to ensure that all of the elements needed to deliver a usable solution are addressed.

As a specific example, the recommendations of the CC/PP working group look to be a well-designed, flexible and comprehensive framework for conveying delivery context, but the level of adoption and awareness of CC/PP has, so far, been disappointing. The author believes that one of the reasons for this has been the absence of a comprehensive standard reference vocabulary.

The current situation is analogous to what could have happened (or not happened) if, back in 1990, the HTTP protocol had been developed but nobody had designed or agreed on a common markup language (HTML).

The point is that when a key link in the chain is missing, it can prevent a solution being adopted because without the chain being whole it is not able to bring about the benefits that it promises. In the opinion of the author, a common vocabulary is the missing link that is holding back the wider adoption of technologies for conveying and interpreting delivery context, especially CC/PP.

Position on Delivery Context

Volantis supports and endorses the work of the W3C DIWG in general, and the recent work on delivery context in particular.

Volantis suggests that the DIWG should consider how a standard vocabulary for all aspects of delivery context could be developed. Such a vocabulary could aim to embrace the semantics of existing domain-specific vocabularies while taking a broader perspective. It should pay particular attention to areas where existing vocabularies are weak, in order to ensure they are well supported in the new vocabulary. In terms of one specific aspect of delivery context, namely device capabilities, the vocabulary should cover a major proportion of the attributes of a wide range of user-agents across all device classes.

A resulting standard vocabulary should:

Note: the basic requirement to be relevant to all device classes, while also being comprehensive and modular suggests that a taxonomy of device types/classes may be needed as a foundation for determining the content of each module.

It goes without saying that a unified delivery context vocabulary will not be easy to create. There will be political and commercial barriers as well as technical ones to be overcome.


Volantis' motivation for participating in the Delivery Context workshop is: